There are five meanings listed in OED's entry for the noun spinster, one of which is considered derogatory. See ‘Meaning & use’ for definitions, usage, and quotation evidence.
Yahoo: The real meaning behind the word "spinster" and the secret ways it's still used today
The real meaning behind the word "spinster" and the secret ways it's still used today
Spinster or old maid is a term referring to an unmarried woman who is older than what is perceived as the prime age range during which women usually marry. It can also indicate that a woman is considered unlikely to ever marry. [1]
"Spinster" wasn't always a criticism. Here's the story of how this term evolved from a label for a person who spun wool and thread for a living to an unfortunate, single, older woman.
By the 17th century, spinster was being used in legal documents to refer to unmarried women. The -ster in spinster sounds modern to our ears—and maybe we can thank hipster for that—but it goes back almost 1000 years.
When encountered in historical documents, ‘spinster has invariably been read by historians as a designation of marital status, since it became in the 17th century the principal identification of a never-married woman, taking over from ‘singlewoman’ and ‘maiden’ or ‘maid.
SPINSTER definition: 1. a woman who is not married, especially a woman who is no longer young and seems unlikely ever to…. Learn more.
A spinster was simply a woman who spun thread or yarn — a common occupation that could be done from home, no expensive looms needed.