Chemically nonreactive (5)
I believe the answer is:
inert
'chemically nonreactive' 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 "dead" , "Sluggish, inactive" , "Disinclined to move" , "Dormant, lifeless" , "Chem. non-reactive" .)