old maid (Noun) — An elderly unmarried woman.
old maid (Noun) — Any of various plants of the genus Zinnia cultivated for their variously and brightly coloured flower heads.
old maid (Noun) — Commonly cultivated Old World woody herb having large pinkish to red flowers.
old maid (Noun) — The loser in a game of old maid.
old maid (Noun) — A card game using a pack of cards from which one queen has been removed; players match cards and the player holding the unmatched queen at the end of the game is the loser (or 'old maid').