Forget name chosen to take on head of government (7)
I believe the answer is:
neglect
'forget' is the definition.
(I know that forget is a kind of neglect)
'name chosen to take on head of government' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'chosen' becomes 'elect' ('elect' as an adjective can mean chosen).
'to take on' means one lot of letters goes inside another.
'head of' indicates taking the first letters.
The initial letter of 'government' is 'g'.
'elect' enclosing 'g' is 'eglect'.
'n'+'eglect'='NEGLECT'
(Other definitions for neglect that I've seen before include "Fail to care for properly" , "Let slide" , "Fail to act or take care" , "Disuse" , "Insufficiently attend to" .)