Colleague gets over some work aversion (7)
I believe the answer is:
allergy
'aversion' is the definition.
(I've seen this before)
'colleague gets over some work' is the wordplay.
'colleague' becomes 'ally' (ally can mean a colleague or associate).
'gets over' indicates putting letters inside (some letters go around or over others).
'some work' becomes 'erg' (an erg is a unit of work done).
'ally' enclosing 'erg' is 'ALLERGY'.
(Other definitions for allergy that I've seen before include "Hypersensitive reaction of the body to a foreign substance" , "Unfavourable reaction to pollen, certain foods etc" , "Antipathy (colloq.)" , "Pathological aversion" , "Strong aversion" .)