недо-

Originally probably не- (ne-) +‎ до- (do-).

• недо-: IPA^(key): [nʲɪdə]
• недо́-: IPA^(key): [nʲɪˈdo] (when stressed in past passive participles and past tense forms)
• не́до-: IPA^(key): [ˈnʲedə] (when stressed in nouns)

недо- • (nedo-)

1. (used with verbs) under-, insufficiently

   ‎недо- (nedo-) + ‎дать (datʹ, “to give”) → ‎недода́ть (nedodátʹ, “to give less than required”)

   ‎недо- (nedo-) + ‎плати́ть (platítʹ, “to pay”) → ‎недоплати́ть (nedoplatítʹ, “to underpay”)

   ‎недо- (nedo-) + ‎стать (statʹ, “to happen, to become”) → ‎недоста́ть (nedostátʹ, “to be insufficient”)

   ‎недо- (nedo-) + ‎ед- (jed-, “to eat”) + ‎-а́ть (-átʹ) → ‎недоеда́ть (nedojedátʹ, “to be undernourished”)

2. (used with verbs) to fail to do

   ‎недо- (nedo-) + ‎де́лать (délatʹ, “to do”) → ‎недоде́лать (nedodélatʹ, “to fail to do, to fail to finish”)

   ‎недо- (nedo-) + ‎смотре́ть (smotrétʹ, “to look at; to look after, to watch”) → ‎недосмотре́ть (nedosmotrétʹ, “to overlook; to fail to look after”)

   ‎недо- (nedo-) + ‎мог- (mog-, “to be able”) + ‎-а́ть (-átʹ) → ‎недомога́ть (nedomogátʹ, “to be unwell, to be indisposed”)

• The stressed variants are found in the following situations:
  1. the past participle of verbs with a one-syllable root ending in -ать: e.g. недо́данный (nedódannyj) from недода́ть (nedodátʹ, “to give insufficiently”);
  2. the past tense of some verbs with a one-syllable root: e.g. недо́дал (nedódal, masculine singular past tense) from недода́ть (nedodátʹ, “to give insufficiently”);
  3. some deverbal and other derived nouns: e.g. не́доросль (nédoroslʹ, “ignorant young man”) from недоро́слый (nedoróslyj, “not full-grown”).