Crossword Genius

Single girl torn apart by old tax: it’s never-ending! (10)

Ross

I believe the answer is:

incessancy

I'm a little stuck... Click here to teach me more about this clue!

'single girl' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'torn apart by old tax it's never-ending' is the wordplay.
I cannot quite see how this works, but
'tax' could be 'cess' (I've seen this in another clue) and 'cess' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Times.
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