alveolus n.

1799, "pertaining to the sockets of the teeth," from a modern medical use of Latin alveolus "socket, small hollow or cavity" (see alveolus) + -ar. Sense extended 19c. to other anatomical hollows.

c. 1300, "joyful song," also a kind of dance in a ring, from Old French carole "kind of dance in a ring, round dance accompanied by singers," a word of uncertain origin. Perhaps from Medieval Latin choraula "a dance to the flute," from Latin choraules "flute-player," from Greek khoraulēs "flute player who accompanies the choral dance," from khoros "chorus" (see chorus) + aulein "to play the flute," from aulos "reed instrument" (see alveolus). OED writes that "a Celtic origin is out of the question." The meaning "Christmas hymn of joy" is attested from c. 1500.

"pertaining to fluids in motion," c. 1600, from French hydraulique, from Latin hydraulicus, from Greek hydraulikos (organon) "water organ," the name of a musical instrument invented by the Egyptian Ctesibius, from hydr-, stem of hydor "water" (from suffixed form of PIE root *wed- (1) "water; wet") + aulos "musical instrument, hollow tube, pipe" (see alveolus). Extended by the Romans to other water engines.