Smart piece of kit uses down link (7)
I believe the answer is:
necktie
'smart piece of kit' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'down link' is the wordplay.
'down' becomes 'neck' (both can mean to finish a drink).
'link' becomes 'tie' (synonyms).
'neck'+'tie'='NECKTIE'
'uses' acts as a link.
Can you help me to learn more?
(Other definitions for necktie that I've seen before include "American garment" , "Ascot?" , "Male dress item (US)" , "one may get collared!" , "one can get knotted" .)