conjugate

The story

1. Latin · derived fromconiugō“to yoke together, combine; (New Latin) to conjugate, decline, inflect”
2. New Latin · borrowed fromconiugātus
3. Middle English · inherited fromconjugat(e)“combined, united”
4. English todayconjugate

The adjective (as “combined, united”) and noun are first attested in 1471, in Middle English, the verb in 1530; partly from Middle English conjugat(e) (“combined, united”), partly directly borrowed from New Latin coniugātus, the perfect passive participle of Latin coniugō (“to yoke together, combine; (New Latin) to conjugate, decline, inflect”) (see -ate (etymology 1, 2 and 3)), from con- (“with”) + iugō (“to join”). In Classical Latin, the word for conjugate (grammar) was dēclīnō, coniugō is a later back-formation from post-classical coniugātiō (“conjugation, declension”).