Sluggish at interchange (5)
I believe the answer is:
'sluggish' is the definition.
'at interchange' is the wordplay.
I cannot quite understand how this works, but
'at' could be 'in' and 'in' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for inert that I've seen before include "Sluggish, still" , "Like some gases" , "Chemically unreactive" , "Without the strength to move" , "Not active or reactive" .)