Do nothing, say, to protect a good name (8)
I believe the answer is:
stagnate
'do nothing' is the definition.
(thesaurus)
'say to protect a good name' is the wordplay.
'say' becomes 'state' ('state' can be a synonym of 'say'**).
'to protect' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'name' becomes 'n' (common abbreviation e.g. on forms).
'a'+'g'+'n'='agn'
'state' going around 'agn' is 'STAGNATE'.
(Other definitions for stagnate that I've seen before include "Do nothing" , "Get stuck" , "Become foul (water)" , "Cease activity" , "(Of water) become motionless" .)