Garbage force brought in to recycle? (6)
I believe the answer is:
refuse
'garbage' is the definition.
(synonyms)
'force brought in to recycle?' is the wordplay.
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'brought in' means one lot of letters goes inside another.
'to recycle?' becomes 'reuse' ('reuse' can be a synonym of 'recycle').
'f' inserted inside 'reuse' is 'REFUSE'.
(Other definitions for refuse that I've seen before include "'Deny, turn down (6)'" , "Reject the waste material" , "Deny; rubbish" , "Turn down, reject" , "Say no to - rubbish" .)