Unusual is a cat embracing mediator (7)
I believe the answer is:
liaison
'mediator' is the definition.
(I've seen this before)
'unusual is a cat embracing' is the wordplay.
'unusual' indicates anagramming the letters.
'cat' becomes 'lion' (lion is a kind of cat).
'embracing' indicates putting letters inside.
'is'+'a'='isa'
'isa' is an anagram of 'ais'.
'ais' going inside 'lion' is 'LIAISON'.
(Other definitions for liaison that I've seen before include "Contact between groups" , "Bond of union" , "Channel of communication" , "Cooperation between people or organisations" , "Illicit romance" .)