Republic occasionally rejected suggestion (4)
I believe the answer is:
clue
'suggestion' is the definition.
(thesaurus)
'republic occasionally rejected' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'rejected' says the letters should be written backwards.
The alternating letters of 'republic' are 'eulc'.
'eulc' in reverse letter order is 'CLUE'.
(Other definitions for clue that I've seen before include "Hint, tip" , "crossword guide" , "Crossword help" , "Hint towards solution" , "Inkling" .)