Choose not to do something (7)
I believe the answer is:
abstain
'choose not to do something' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for abstain that I've seen before include "Resist" , "Do without, as in lent" , "Refrain (from drink)" , "Forego,do without" , "Formally decline to vote" .)