spinster

Concise Oxford English Dictionary © 2008 Oxford University Press:
spinster/ˈspɪnstə(r)/

▶noun chiefly derogatory an unmarried woman, typically an older woman beyond the usual age for marriage.

– derivatives
spinsterhood noun,
spinsterish adjective.

– origin ME (in the sense ‘woman who spins’): from spin + -ster.