"to reflect, ponder, meditate; to be absorbed in thought," mid-14c., from Old French muser (12c.) "to ponder, dream, wonder; loiter, waste time," which is of uncertain origin; the explanation in Diez and Skeat is literally "to stand with one's nose in the air" (or, possibly, "to sniff about" like a dog who has lost the scent), from muse "muzzle," from Gallo-Roman *musa "snout," itself a word of unknown origin. The modern word probably has been influenced in sense by muse (n.). Related: Mused; musing.
late 14c., "one of the nine Muses of classical mythology," daughters of Zeus and Mnemosyne, protectors of the arts; from Old French Muse and directly from Latin Musa, from Greek Mousa, "the Muse," also "music, song," ultimately from PIE root *men- (1) "to think." Meaning "inspiring goddess of a particular poet" (with a lower-case m-) is from late 14c.
The traditional names and specialties of the nine Muses are: Calliope (epic poetry), Clio (history), Erato (love poetry, lyric art), Euterpe (music, especially flute), Melpomene (tragedy), Polymnia (hymns), Terpsichore (dance), Thalia (comedy), Urania (astronomy).