The definition of a spinster is an unmarried, middle-aged or older woman, or a woman who is divorced or widowed.(noun)
An example of a spinster is a woman in her sixties who lives alone.
See spinster in Webster's New World College Dictionary
Origin: ME < spinnen, to spin + -ster
See spinster in American Heritage Dictionary 4
Origin: Middle English spinnestere, female spinner of thread
Origin: : spinnen, to spin; see spin
Origin: + -estere, -ster, -ster.
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