Support nearly everything within the law (5)
I believe the answer is:
legal
'within the law' is the definition.
(I've seen this in another clue)
'support nearly everything' is the wordplay.
'support' becomes 'leg' (leg is a kind of support).
'nearly' means to remove the last letter.
'everything' becomes 'all' (all things).
'all' with its last letter taken off is 'al'.
'leg'+'al'='LEGAL'
(Other definitions for legal that I've seen before include "Sound" , "not banned" , "within the rules" , "In accordance with law" , "Referring to the law" .)