Affair of big cat crossing road with last of cubs (7)
I believe the answer is:
liaison
'affair' is the definition.
(synonyms)
'big cat crossing road with last of cubs' is the wordplay.
'big cat' becomes 'lion' (lion is a kind of big cat).
'crossing' indicates putting letters inside.
'road' becomes 'ai' (I've seen this in other clues).
'with' is a charade indicator (letters next to each other).
'last of' indicates one should take the final letters.
The final letter of 'cubs' is 's'.
'ai'+'s'='ais'
'lion' placed around 'ais' is 'LIAISON'.
'of' acts as a link.
(Other definitions for liaison that I've seen before include "Go-between" , "Intimate relationship" , "Amour; communication" , "Intermediary" , "Contact between groups" .)