Like a noble gas (5)
I believe the answer is:
inert
'like a noble gas' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for inert that I've seen before include "like neon" , "Indolent - unreactive" , "Slow and apathetic" , "Like some gases" , "Unable to move or resist motion" .)