kind of swallow-like bird (Chelidon urbica), 1580s (earlier in diminutive form maretinet, mid-15c.), from Old French martin, which is apparently from the masc. proper name Martin in some sense. Writers in 17c. said it was named for St. Martin of Tours (d. 397 C.E.), patron saint of France, whose festival day (Martinmas) is Nov. 11, about the time the birds are said to depart for winter. But OED says the naming "may have been purely arbitrary," and Century Dictionary says "the name has no specific meaning ...." Usually with a qualifying term: the common house-martin is so called because it nests under the eaves of houses. The American purple martin is so called by 1804.
masc. proper name, from Latin Martinus, derivative of Mars (genitive Martis), Roman god of war (see Mars). In Elizabethan times, the parish of St. Martin-le-Grand in London was "celebrated as the resort of dealers in imitation jewellery" [OED].