Если говорить об "arūpa", то вариант "бестелесный" кажется мне более понятным, чем "бесформенный", который в русском занят несколько другим смыслом:
БЕСТЕЛЕ́СНЫЙ, бестелесная, бестелесное; бестелесен, бестелесна, бестелесно (книжн.). Нематериальный, бесплотный.
БЕСФО́РМЕННЫЙ, бесформенная, бесформенное; (кратк. мужск. не употр.) бесформенна, бесформенно. Не имеющий определенных очертаний, форм, расплывчатый, хаотический. Тело, раздавленное поездом, превратилось в бесформенную массу. Художник старался зарисовать свои бесформенные видения.
Толковый словарь Ушакова. Д.Н. Ушаков. 1935-1940.
Однако тут еще надо разобраться, когда какой вариант применим.
Из "Критического словаря пали":
a-rūpa, mfn. (resp. n. subst.) [ts.], formless, incorporeal, immaterial (cf. arūpi(n) & āruppa), mostly n. sg. pl. incorporeal existence & immaterial things; sg. ~aṁ, given as a synon, of nibbāna: Abh 6, Sadd 70,25*, Abhidh-av 82,19*; - Abhidh-av 72,15; 100,10*, etc.; Rūpārūp 151,3; voc. ~a dūraṁgama ekacāri, Th 1122 (scil. citta); acc. ~aṁ (manasikaroto), DN III 240,22; do. sg. & pl., Yam I 19,21, etc., etc.; abl. ~ā (rūpā + . . . pamuccati), Ud 9,8* (Ud-a); Abhidh-av 40,24*-29*; loc. ~e upapatti = arūp[ū/u]papatti (q. v.), As 200,28; ~e (opp. rūpa-°), MN I 410,30; Abhidh-av 72,12; 16*; pl. abl. ~ehi, It 62,2 (~nirodho santataro; lt-a Ee reads āruppehi. cf. Sn p. 147,1); loc. ~esu susaṇṭhitā, Sn 755 (v. l. asaṇṭhitā) ≠ It 62,9* (~esu asaṇṭhitā; It-a (Ee) reads āruppesu);~esu cittaṁ pakkhandati, etc., DN III 240,23; Abhidh-av 71,23* (pākaṭā rūpa-dhammesu, ~ apākaṭā);
- m. ~o, Ps II 101,1 (= 'arūpī', scil. ākāso); As 200,28 (= arūpa-bhavo [w. r. °-bhāvo]); ~o atta-paṭilābho, DN I 195,22 (opp. oḷāriko and manomayo); m. pl. ~ā (dhammā), AN I 83,2 (opp. sa-rūpā); - ifc. v. rūpârūpa (Abhidh-av 47,19*; °-bhava, Vibh-a 185,22 foll.; Saddh 228; 480; °-vipāka, Abhidh-av 47,13*).
- - °-ka, mfn. = a-rūpa, (a-cittaka +), Yam I 60,7 foll. etc. etc.;
- °-kammaṭṭhāna, n., meditation on a°; ~aṁ kathento vedanāvasena kathesi, Ps I 275,28 ≠ Sv (III) 774,19, cf. 724,8-20;
- °-kasiṇa-lābhi(n), mfn., possessed of (or mastering) a° as an object for meditation; acc. ~iṁ (= 'arūpiṁ'), Sv (II) 505,14;
- °-kāyika, mfn., belonging to the class of formless beings; m. pl. ~ā nāma devā, Mil 317,12 (cf. Trsl. II 187 n. 3);
- °-kusala, mfn., skilled in a°; n. ~aṁ, Abhidh-av 46,12*; m. pl. ~ā, ib. 40,22*;
- °-kkhandha, m. pl. ~ā, the incorporeal groups, i. e. pañca kkhandhā except rūpa; ~ā
hi idha 'bhavo' ti āgatā, Vibh-a 206,6; cattāro ~ā, Spk II 109,31; Ps I 73,6 (cf. Mp II 280,6: vedanâdayo . . . tayo ~ā); gen. pl. ~ānaṁ, Tikap-a 67,14; tiṇṇaṁ ~ānaṁ, Vism 488,9;
- °-kkhandha-gocara, mfn., having arūpa-kkhandhā as objects; acc. m. ~aṁ ( = 'arūpiṁ'), Sv (II) 505,14;
- [°-gāmi(n), mfn., bound for a°; m. pl. ~ino, It 62,5* (unmetr. v. l. for āruppa-(ṭ)ṭhāyino) = SN I 131,13* = 133,1*];
- °-jīvita, n., incorporeal form of life(?); loc. ~e, Abhidh-av 68,35*;
- °-jjhāna, n., meditation on a°; acc. ~aṁ (patvā), Vism 659,24 (mhṭ: catubbidhaṁ ~aṁ); gen. ~assa ālambā caturo matā, Saddh 464 (scil. ākāso, etc.); pl. ~āni, Sv I 219,27 (opp. rūpa-jjhānāni) ≠ (II) 387,22; cattāri ~āni, title of Dhs 265-68; °-jjhāna-lābhi(n), mfn., having mastered them, Sv I 219,24);
- [°-ṭṭhāyi(n), mfn., dwelling in the arupa-(brahma-) loka; w. r. for āruppa°; m. pl. ~ino, It 62,5* (- - ˇ - ˇ - ; v. ll. °-vāsino & °-gāmino) = Sn 754 (reading āruppavāsino, but Bi °ṭṭhāyino) = SN I 131,13* (reading āruppa-ṭṭhāyino, v. l. arūpa-gāmino)];
- °-taṇhā, f., thirst for a° (existence in the formless sphere), DN III 216,5 (rūpa-taṇhā ~ā nirodha-taṇhā; Sv) = Nidd I 9,1 (- arūpabhave taṇhā, Nidd-a); Vibh (365,32) 366,4-6;
- °-dhamma, m., 'things' beyond the rūpa-sphere; pl. ~ā, Mp II 279,12 (324 ~ā, opp. 66 rūpa-dhammā); As 347,14; Tikap-a 26,6; 67,15; loc. pl. ~esu, ib. 54,14;
- °-dhātu, f. (cf. sa. ārūpya-dh°) the element (plane) of a°; acc. ~uṁ (kāma-dhātuṁ +), Nidd I 60,23 (= arūpa-bhavaṁ, Nidd-a); Paṭis I 137,35 (do.); loc. ~uyā (kāma-dhātuyā+), Vibh 406,28-407,31; do. Yam I 268,13, etc.; do. Pj II 507,20 (tividhāya); nom.pl. tisso dhātuyo: kāma-dhātu rūpa-dh° arūpa-dh°, DN III 215,20 = 275,23 = MN III 63,7; do. tisso dhātuyo: rūpa-dh° arūpa-dh° nirodha-dh°, It 45,22 = DN III 215,21 (cf. Nett 97,20); loc.pl. ~usu, Th 259 (rūpadhātusu + ; = arūpa-bhavesu, Th-a);
- °-dhātu-kathā, f., title of Kv VIII, 6 (p. 372-74);
- °-dhātu-paṭisaṁyutta, mfn., relative to arūpa-dhātu; m. ~o rāgo sārāgo (scil. arūpa-taṇhā), Vibh 366,5; pl. ~ā, Sv (III) 988,15;
- °-dhātu-vepakka, mfn., ripening in a°-dh°; n. ~aṁ (kammaṁ), AN I 223,34 foll. (see Mp II 334,15);
- °-paccaya, m., (causal) relation to a°; acc. ~aṁ vinā, Tikap-a 26,4 foll.;
- °-pariggaha, m., grasping of a°; ~o, Ps I 275,31 = Sv (III) 721,36; Ps IV 104,14;
- °-puñña, n., merit in a°; pl. ~āni, Abhidh-av 40,27*; yāni c' ~āni sarūpen' īritāni, ib. 100,4*;
- °-ppaṭisaṁyutta, mfn., relative to a°; m. ~o, Paṭis II 41,5 (vimokkho), cf. arūpa-dhātu-paṭisaṁyutta above;
- °-brahma-lokā, m.pl., the four immaterial Brahma worlds, Childers referring only to Burnouf Lotus 811; MTD App. p.253 (ākāsânañcâyatana (q. v.) + ; DN II 156,8 foll.; cf. Ps V 56,5 & arūpâvacara below);
- °-bhava, m., formless existence (in the Arūpabrahmaloka); ~o, AN I 223,35 foll.; kāma-bhavo rūpa-bhavo ~o, DN II 57,22; III 216,10; SN II 3,11; IV 258,28; AN III 444,18; Vibh 137,8 quoted Vism 571,29; ~o nāmokāso nāma, Tikap-a 26,1 foll.; Dhātuk 15,4; acc. ~aṁ, Nidd-a Ee I 188,35 ( = 'arūpadhātuṁ'); dat. ~āya, AN IV 404,10; loc. ~e nibbattissāmi, Ja I 55,4; ~e (kāmabhave + ), Nidd I 48,1; ~e chanda-rāgo arūpa-taṇhā, Sv (III) 988,19; ~e taṇhā, Nidd-a Ee I 41,17 (= 'arūpa-taṇhā'); ~e avijjā ~e saṅkhārānaṁ paccayo hoti, Vism 199,2; ~asmiṁ, Vibh-a 204,23; dve~ā,Vibh-a 185,23; - [°-bhāva, m., As 200,28 read arūpa-bhavo];
- °-magga-samaṅgi(n), mfn., possessed of the way of a°; m. ~ī, Nidd I 280,14 (= arūpasamāpattiyā gamanamaggena aparihīno, Nidd-a);
- °-rāga, m., lust after a°; r[ū/u]pa-rāgo + ~o, DN III 234,20 ≠ Paṭis II 95,3; acc. ~aṁ, AN III 422,16-25 (kāma-r°, rūpa-r° +); abl. ~ā, Paṭis II 37,9; 142,12 foll.; Nidd I 27,21 (= arūpabhave chandarāgā, Nidd-a); ~o arūpadhātu-pariyāpanno ti kathā, title of Kv XVI 10 (p.539- 541);
- °-loka, m., the world of the formless; loc. ~e pi saṅgam apahāya, Saddh 494; ~e pana rūpam eva n'atthi, Rūpārūp 150,30:
- °-vavattha-bhāva-dukkara-pañha, m., title of Mil 87,20 (only in Se;);
- [°-vāsi(n), dwelling in a°; m. pl. ~ino, Sn 754 = It 62,5* (reading °-ṭṭhāyino, q. v.)];
- °-vipāka, mfn., being a "result of" a°; n. pl. cattāri ~āni (scil. catubbidhaṁ viññāṇaṁ), Vibh-a 152,3 = Vism 546,10;
- °-vibhāga, m., title of a section in Rūpārūp p. 151-59;
- °-samkhāta, mfn., called incorporeal; m. ~o attā, As 360,22; f. ~ā dhātu, Nidd-a (Ee) I 44,18 (= 'arūpa-dhātu');
- °-saññi(n), mfn., neg. of rūpa-saññi(n) = not having the perception of form; m. ajjhattaṁ ~ī, DN II 110,15 foll. = III 260,15 foll. = AN I 40,17 foll. ≠ Dhs 204 foll.; MN II 12,32 ≠ III 222,13; Ud 71,11* (Ud-a 349,6 foll.);
- °-santati, f., immaterial continuity; rūpa-santati +, As 420,15 = Vism 431,30 (quoting the Saṁyutta-bhāṇakas);
- °-samāpatti, f., "attainment" of a°; instr. ~iyā, Nidd-a ad Nidd I 280,14; ~iyā rūpakāyato vimutto, Sv (II) 514,4 = Ps III 188,8 = Mp ad AN IV 10,26 ≠Pp-a 191,2; °-nimittaṁ, ind., Sv I 119,10; pl. catasso ~iyo, Paṭis II 40,17-41,28; As 209,23 = Vism 338,29 (reading āruppa-°), cf. Abhidh-av 103,23*-24*; gen. pl. catunnaṁ ~īnaṁ ekekato vutthāya, Ps III 188,9 = Mp ad AN IV 10,26 ≠ Pp-a 191,9; As 202,16; Nidd I 280,6-7;
- °-sammasana-naya, m., title of Vism 617,17-618,12;
- °-sahagata, mfn., accompanied by (the idea of) a°; gen. pl. ~ānaṁ samāpattīnaṁ (scil. lābhī), Pp 11,14 foll. (Pp-a) - 62,3 foll. (Pp-a), quoted Sadd 465,17;
- "ârammaṇa, mfn., having a° for object (of meditation); n. ~aṁ(sukhaṁ; opp. rūpârammaṇa), AN I 82,12-14;
- °âvacara (1) m. - arūpa-brahmaloka; Yam I 119,1-2; loc. ~e, Yam I 66,9; 232,31-233,3; II 82,34 foll.; - (2) mfn., related to, experienced in, or frequenting the realm of formlessness; m. ~o (phasso), Nidd I 52,20; 222,26 (Nidd-a); Tikap-a 27,8 (kāmâvacaro +, scil. kiriyahetu); f. ~ā bhūmi, Paṭis I 83,28 (kāmâvacarā bhūmi +); n. ~aṁ (cittaṁ), Abhidh-s 1,9; Abhidh-av 14,19; Vism 453,28 (cf. 452,30); gen. ~assa kusalassa kammassa, Dhs 502-3; m. pl. ~ā, It-a II 42,16 (= 'āruppa-tthāyino'); ~ā (dhammā), Dhs 1260; 1265; 1281, etc.'; 1284 (As 388,8); Nidd I 2,3; Paṭis I 101,17; 132,24 (acc. pl. ~e dhamme); II 230,8; ~ā (vipākā), Dhs 1037; m. gen. pl. ~ānaṁ: Yam I 71,33; 72,5; - (3) do. mfn. in several cpd.s;
°-kusala, n., Dhs p. 60,3 (title of Dhs 273-76),
°-kusalāni, Nāmar-s 3,14; 4,4;
°-kusala-cittāni, Abhidh-s 3,24 (cattāri); dvādasa °-kusala-vipāka-kriyā-cittāni, ib. 4,6;
°-kriyā-cittāni; ib. 4,5 (cattāri); Abhidh-av 14,1-4; Nāmar-s 6,9;
°-devatā, Sv(II) 678,5;
°-loka, Ps III 122,29;
°-vipāka-cittāni (cattāri), Abhidh-s 4,2; Nāmar-s 5,25;
°jjhāna, n., Ud-a 186,22 (catubbidhaṁ); Sv (II) 514,14;
°-paṭisandhi, f., Abhidh-s 22,2 (apāya-p° +);
°-samādhi-bhāvanā-niddesa, m., title of Abhidh-av etc XV (p. 100-103);
°-samāpatti, f., "attainment" of a°; gen. ~iyā lābhī, Pp 38,3; pl. ~iyo (catasso), Paṭis I 85,16; °-hetu, m.; pl. cha ~ū, Dhs 1053 ("the six causes operative in a°").
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