-phile

1920, used of milk fermented by acidophilic bacteria, from acidophil (1900), indicating "easily stained by acid dyes," a hybrid word, from Latin acidus "acidic, sour, tart" (see acid (adj.)) + Greek philos "loving" (see -phile); the bacteria so called because they stain easily with an acid dye.

"cat-lover," 1931, with -phile "one that loves" + Greek ailouros "cat" (probably only "wildcat," as "domestic cats were not found in the Greek world" [Beekes]), which is of unknown origin. Usually explained as a compound of aiolos "quick-moving" + oura "tail," hence "with moving tail," which is plausible despite some phonetic difficulties, according to Beekes, who also notes "the word may well have been adapted by folk etymology ...." An earlier attempt at an English word for "cat-lover" was philofelist (1843).