One gives a convict life, as an interim measure (4,2,9)

'one' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'a convict life as an interim measure' is the wordplay.
I cannot quite see how this works, but
'a' is found in the answer.
'an' could be 'i' (Roman numeral for one) and 'i' is found within the answer.
'measure' could be 'ton' (ton is a kind of measure) and 'ton' is located in the leftover letters.
This explanation may well be incorrect...

'gives' acts as a link.