This is the answer! (4)
I believe the answer is:
clue
I believe this clue is a double definition.
'this' is the first definition.
(the clue referring to itself!)
'the answer' is the second definition.
(thesaurus)
'is' acts as a link.
(Other definitions for clue that I've seen before include "For example, this" , "Crossword hint?" , "contribution to crossword" , "Pointer" , "crossword guide" .)