出典:Wiktionary
Ultimately from Proto-Indo-European *lewg- (“bend, twist”) (whence also lū̆xus, -a, -um (“dislocated”) and lū̆xus, -ūs (“dislocation; splendor”)).
Cognate with Ancient Greek λύγος (lúgos), Lithuanian lugnas, and Old Norse lykna. Compare with English louk; lock.
Per De Vaan, formed as a frequentative from Proto-Italic *luktos, the perfect passive participle form of an unattested non-frequentative verb. De Vaan assumes the stem had a short vowel here and in lū̆xus, despite noting that this is difficult to explain as the word meets the conditions for Lachmann's law to apply; he speculates that a hypothetical nasal present stem (which would regularly have had a short vowel), as found in Celtic, could have exerted analogical influence on the vowel length.[1]
lū̆ctor (present infinitive lū̆ctārī または lū̆ctārier, perfect active lū̆ctātus sum); first conjugation, deponent
1The present passive infinitive in -ier is a rare poetic form which is attested.