didn't read the whole thread, but can you help out this non-native speaker? I just heard the word 'spinster' used matter-of-factly in a documentary. I always thought it was an old fashioned word that is now not much more than a derogative term (or for fun, such as with a thread here on ehell, but I suppose it's different when people own the word?).
Is it still used? Or rather avoided?
It's rather an old-fashioned word now, since the circumstances of family life have changed.
A 'spinster' was an unmarried woman. The word implied that she was a woman that no one wanted to marry, or one who was so picky about prospective husbands that she refused to get married. Up until the 20th Century, that usually meant that she had to live with family members her whole life; her parents as long as they lived, her brother's family or nephew's family or some other (male) relative. It would have been scandalous for her to live alone in her own home! What, no man to keep her in line?

Who knows what she might do!

She was tolerated as long as she made herself useful. "Spinster" originally meant that, freed of the need to care for children of her own, she had the time and inclination to spin thread for sale, thus changing her from a useless mouth to feed into someone who brought money into the family. After the Industrial Revolution, the name stuck but the occupation ceased to exist.
As the 20th Century advanced and independence for women became common, 'spinster' and the early 20th Century 'bachelor girl' for an unmarried woman fell out of fashion. If your friend/sister/aunt isn't married, she would simply be described as single.