Etymology
1. Per Derksen, from the root of *nicь (“lying face downwards”), from Proto-Indo-European *ni-h₃kʷo- with the Slavic progressive palatalization, from the root *ní. Cognate with Sanskrit नि (ni, “downwards”), नीचा (nīcā́, “downwards”).
2. Per Vasmer, there are two etymologically separate verbs here, one with the approximate meaning "to droop, to wilt" and coming from the root of *nicь as above, and another with the approximate meaning "to arise, to penetrate" from a different root:
3. * The former is cognate with Lithuanian nỹkti (“to disappear, perish”) and Latvian nikt (“to suffer; to wear out”).
4. * The latter is cognate with Lithuanian ni̇̀kti (“to glow”) (1sg. ninkù, 1sg. past nikaũ), įni̇̀kti į̇̃ dárbą (“to plunge headlong into work”), apni̇̀kti (“to attack”), etc., as well as Old Prussian neikaut (“to walk, to wander”), Latvian niktiês (“to impose oneself”), nikns (“fierce, wicked”), nàiks (“fierce, wicked, angry, quick”), and Ancient Greek νεῖκος (neîkos, “quarrel, dispute”), νεικέω (neikéō, “to quarrel, to attack”), νῑ́κη (nī́kē, “victory”), νῑκάω (nīkáō, “to win”).
Verbs referencing "niknǫti"
Albanian
nis, Serbo-Croatian
niknuti, Serbo-Croatian
никнути, Ukrainian
никнути, Russian
никнуть, Macedonian
никне, Lithuanian
nykti.