old maid

noun

1. An old woman who has never married; a spinster.

   If she is looking for the perfect man before she marries, she'll be an old maid.

2. The Madagascar periwinkle.

3. The common zinnia.

4. An unpopped kernel in a batch of popped popcorn kernels.

5. A card game in which cards must be paired and one undesirable card is designated "old maid".

6. The unmatchable card in that game.