Agent sat around to be still (8)
I believe the answer is:
stagnate
'be still' is the definition.
(thesaurus)
'agent sat around' is the wordplay.
'around' indicates an anagram.
'agent'+'sat'='agentsat'
'agentsat' is an anagram of 'STAGNATE'.
'to' acts as a link.
(Other definitions for stagnate that I've seen before include "resemble pond water?" , "Cease to flow or move" , "Show little activity" , "Stop shifting" , "turn foul" .)