Leave current unit after month (6)
I believe the answer is:
decamp
'leave' is the definition.
(decamping is a kind of leaving)
'current unit after month' is the wordplay.
'current unit' becomes 'amp' (amp is a kind of current unit**).
'after' means one lot of letters go next to another.
'month' becomes 'dec' (Dec is an example).
'amp' after 'dec' is 'DECAMP'.
(Other definitions for decamp that I've seen before include "Fold tents and go" , "Make off - from tent?" , "Mizzle" , "Go away suddenly or secretly - leaving tent?" , "Split" .)