Syrup that could make cat reel! (7)
I believe the answer is:
treacle
'syrup' is the definition.
(I know that treacle is a type of syrup)
'could make cat reel' is the wordplay.
'could make' indicates an anagram.
'cat'+'reel'='catreel'
'catreel' anagrammed gives 'TREACLE'.
'that' is the link.
(Other definitions for treacle that I've seen before include "Contrived sentimentality - sticky substance" , "flattery" , "Carroll's sisters had to live with" , "Viscous liquid" , "Something sticky" .)