Former partner is beginning to enjoy acquiring fresh skill (9)
I believe the answer is:
expertise
'skill' is the definition.
(I have seen 'Technical skill' mean 'expertise' so perhaps 'skill' could also mean 'expertise')
'former partner is beginning to enjoy acquiring fresh' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'beginning to' indicates taking the first letters.
'acquiring' is an insertion indicator.
'fresh' becomes 'pert' (I've seen this before).
The first letter of 'enjoy' is 'e'.
'ex'+'is'+'e'='exise'
'exise' placed around 'pert' is 'EXPERTISE'.
(Other definitions for expertise that I've seen before include "professionalism" , "Skill or knowledge in a particular field" , "Thorough knowledge" , "Craft" , "Adroitness" .)