Crossword Genius

Ending in jail, I am afraid of getting no answer — am I there for ever? (5)

Ross

I believe the answer is:

lifer

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

I don't understand the rest of the clue.

(Other definitions for lifer that I've seen before include "One given lots of porridge" , "person given sizeable bird" , "One with maximum sentence" , "Serious criminal" , "One behind bars for ever" .)

I've seen this clue in The Times.
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