'Tenor' is Latin for 'the holder' — the voice that 'held' the melody in medieval polyphony.
The highest of the ordinary adult male singing voice; the general meaning or character of something.
From Old French tenour, from Latin tenor (a holding on, a continuous course, the general drift), from tenēre (to hold). The PIE root is *ten- (to stretch, to hold). In medieval musical theory, the tenor was the voice part that held the cantus firmus — the principal melody upon which counterpoint was built. Literally the holding voice, it was so named because it sustained the given tune while other voices wove around it. From the 13th century the term designated the voice range above bass that most naturally sustained long notes; by the 16th century it referred to the
The 'tenor' of a conversation and the 'tenor' who sings are the same word — both mean 'holding.' The vocal tenor 'held' the main melody in medieval polyphony. The 'tenor' of a discussion is its 'holding course' — its general direction and meaning. And 'lieutenant' literally means 'place-holder' (lieu + tenant). The most common PIE root in English, *ten-, connects singing, meaning, and military rank.