nokʷt-

The noun *nokʷt- ("night") forms one of the most celebrated cognate sets in Indo-European studies. The phonological correspondences are entirely regular across every major branch, and the word appears in all introductory treatments of the comparative method. Latin nox (genitive noctis) continues the root directly. Derivatives include nocturnal, nocturne, equinox (aequinoctium, "equal night"), and the liturgical term nocturn. Greek nýx (νύξ, genitive nyktós) shows the expected development. The variant form nykterís ("bat," literally "night creature") and the compound nyktalōpía ("night blindness," whence nyctalopia) derive from this root. Sanskrit nák (in the accusative nákta, "by night") and the compound nákṣatra ("star," literally "night-thing") show the Indo-Iranian reflex. The semantic development from "night" to "star" (the things associated with night) is noteworthy. Gothic nahts, Old English niht (Modern English night), Old High German naht (Modern German Nacht), and Old Norse nótt show the Germanic development with Grimm's Law: *k > h (the labialised *kʷ loses its labialisation before a consonant). Lithuanian naktìs and Old Church Slavonic noštĭ continue the Balto-Slavic reflexes. Old Irish in-nocht ("tonight") and Welsh nos preserve the Celtic forms. Hittite nekuz (genitive of the word for "evening") extends the attestation to the earliest-attested IE branch. The consistency of *nokʷt- across branches makes it a diagnostic form for establishing phonological correspondences. Together with *h₂ews- ("dawn") and *deyew- ("sky, day"), it forms part of the reconstructable PIE vocabulary for the divisions of the diurnal cycle.