दुस्-

• दुः- (duḥ-) — before श्, ष्, स् (ś, ṣ, s) and rarely before क्, ख्, प्, फ् (k, kh, p, ph)
  • दुᳶ- (duf-) — (upadhmānīya) optionally before प्, फ् (p, ph)
  • दुᳵ- (dux-) — (jihvāmūlīya) optionally before क्, ख् (k, kh)
• दुर्- (dur-) — before vowels and voiced consonants
• दुश्- (duś-) — before च्, छ् (c, ch) and rarely before श् (ś)
• दुष्- (duṣ-) — before क्, ख्, प्, फ् (k, kh, p, ph) and rarely before ष् (ṣ); in older language also before त्, थ् (t, th) which become ट्, ठ् (ṭ, ṭh)
• दू- (dū-) — before र् (r) and sometimes before द्, ध्, न् (d, dh, n), which become ड्, ढ्, ण् (ḍ, ḍh, ṇ)

From Proto-Indo-Iranian *duš-, from Proto-Indo-European *dus-. Cognate with Ancient Greek δυσ- (dus-, “hard, difficult”), Old Armenian տ- (t-, a negative prefix), Avestan 𐬛𐬎𐬱- (duš-), Gothic 𐍄𐌿𐌶- (tuz-); Old Irish do-.

• (Vedic) IPA^(key): /dus/
• (Classical Sanskrit) IPA^(key): /d̪us̪/

दुस्- • (dus-)

1. ill-, mal-
2. badly, hardly; slight, inferior, etc., often = English in- or un-.

   ‎दुस्- (dus-) + ‎कर्म (karma, “act, action”) → ‎दुष्कर्म (duṣkarma, “evil act”)

• सु- (su-)

• Monier Williams (1899) “दुस्-”, in A Sanskrit–English Dictionary, , new edition, Oxford: At the Clarendon Press, →OCLC, page 488/1.
• Mayrhofer, Manfred (1992) Etymologisches Wörterbuch des Altindoarischen [Etymological Dictionary of Old Indo-Aryan]‎ (in German), volume 1, Heidelberg: Carl Winter Universitätsverlag, pages 735-6