old maid

Short definition from Wiktionary

Noun

1. 1
   An old woman who has never married; a spinster.
2. 2
   The Madagascar periwinkle.
3. 3
   The common zinnia.
4. 4
   An unpopped kernel in a batch of popped popcorn kernels.
5. 5
   A card game in which cards must be paired and one undesirable card is designated "old maid".
6. 6
   The unmatchable card in that game.
7. 7
   A children's card game, sometimes played with a special deck, where the object of the game is for each player to find matches for all the cards in his hand, without being stuck with the single unmatchable card.
8. 8
   The unmatchable card itself.