Where does “poisson chauve-souris” come from?

poisson chauve-souris (French) comes from French Poisson, from Middle French poisson, from Old French poisson, from Old French peis, from Vulgar Latin pesum, from Latin pēnsum, from Latin pendō, from Proto-Italic pendō — to stretch.

Ancestry of “poisson chauve-souris”, step by step

poisson chauve-souris traces back through two separate lines of ancestry.

via French Poisson

StepLanguageWordMeaning
1FrenchPoissonfish marine animal
2Middle Frenchpoissonfish
3Old Frenchpoissonfish
4Old FrenchpeisAlternative form of pais; Alternative form of...
5Vulgar Latinpesum
6Latinpēnsumallotment, portion, weight (of wool measured out to a slave to spin in a day)
7Latinpendōto weigh, weigh out
8Proto-Italicpendōhang, put in a hanging position
9Proto-Indo-European(s)péndeti
10Proto-Indo-European(s)pend-to stretch

via French chauve-souris

StepLanguageWordMeaning
1Frenchchauve-sourisbat
Every word from Proto-Indo-European (s)pend-