Not chemically reactive (5)
I believe the answer is:
inert
'not chemically reactive' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for inert that I've seen before include "(Chem.) not reactive" , "Motionless or lifeless" , "Motionless, still" , "Sluggish - unresponsive" , "Slow and apathetic" .)