Spread in favour of career allowance (13)
I believe the answer is:
proliferation
'spread' is the definition.
(thesaurus)
'in favour of career allowance' is the wordplay.
'in favour of' becomes 'pro' (being pro a particular cause).
'career' becomes 'life' (career can mean someone's life or past).
'allowance' becomes 'ration' (I've seen this before).
'pro'+'life'+'ration'='PROLIFERATION'
(Other definitions for proliferation that I've seen before include "Increase (of nuclear weapons)" , "Increase in numbers" .)