Avoid retirement so as to fill a gap (4,2)
I believe the answer is:
stop up
'fill a gap' is the definition.
'stop up' can be an answer for 'fill' (thesaurus). I am not certain of the 'a gap' bit.
'avoid retirement so as to' is the wordplay.
I cannot quite see how this works, but
'to' is within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stop up that I've seen before include "Don't retire here" , "close" , "Don't go to bed early" , "Block (eg an earth)" , "Cork" .)