Honk endlessly and excessively (3)
I believe the answer is:
too
'excessively' is the definition.
(to too great a degree)
'honk endlessly' is the wordplay.
'honk' becomes 'toot' (synonyms).
'endlessly' means to remove the last letter.
'toot' with its final letter removed is 'TOO'.
'and' is the link.
(Other definitions for too that I've seen before include "Moreover, in addition" , "As well, also" , "Additionally" , "As well; in addition" , "Excessively" .)