Sluggish at interchange (5)
I believe the answer is:
inert
'sluggish' is the definition.
(synonyms)
'at interchange' is the wordplay.
I cannot really see how this works, but
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is found within the answer.
This explanation may well be incorrect...
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" .)