Then of course, there's also spinster and dowager.
But why do single older women seem to have several nomenclatures when single men of any age are simply relegated to bachelor or confirmed bachelor?
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Ah but, dowager is completely different to spinster.

A spinster is a single woman who has never married.

A dowager is used to refer to a lady of the aristocracy whose husband has died. She only had the title by virtue of being married to the Lord/Duke/whatever. Once he died the title is passed to the first born son. Because this has happened she no longer has the right to be known as 'Lady So-and-so' - that is now her son's wife. Instead, she becomes 'The Dowager Lady So-and-so'.

Obviously this never occurs for a man, because once he's died the title passes to the son and if his wife dies it doesn't make any difference because titles pass down the male line.