Former working nurse finally gets prison sentence (3-4)
I believe the answer is:
one-time
'former' is the definition.
(I've seen this before)
'working nurse finally gets prison sentence' is the subsidiary indication.
'working' becomes 'on'.
'finally' says to take the final letters.
'gets' is a charade indicator (letters next to each other).
'prison sentence' becomes 'time' (I've seen this before).
The final letter of 'nurse' is 'e'.
'on'+'e'+'time'='onetime'
(Other definitions for one-time that I've seen before include "Relating to a single occasion" , "Former" .)