Old English modor "female parent," from Proto-Germanic *mōdēr (source also of Old Saxon modar, Old Frisian moder, Old Norse moðir, Danish moder, Dutch moeder, Old High German muoter, German Mutter), from PIE *mater- "mother" (source also of Latin mater, Old Irish mathir, Lithuanian motė, Sanskrit matar-, Greek meter, Old Church Slavonic mati), "[b]ased ultimately on the baby-talk form *mā- (2); with the kinship term suffix *-ter-" [Watkins]. Spelling with -th- dates from early 16c., though that pronunciation is probably older (see father (n.)).
Mother nature first attested c. 1600; mother earth is from 1580s. Mother tongue "one's native language" first attested late 14c. Mother of all ________ 1991, is Gulf War slang, from Saddam Hussein's use in reference to the coming battle; it is an Arabic idiom (as well as an English one), for instance Ayesha, second wife of Muhammad, is known as Mother of Believers. Mother Carey's chickens is late 18c. sailors' nickname for storm petrels, or for snowflakes. Mother lode in the figurative sense is attested by c. 1882, from mining (1849); see lode.