Endlessly watch contest (3)
I believe the answer is:
vie
'contest' is the definition.
(I've seen this before)
'endlessly watch' is the wordplay.
'endlessly' means to remove the last letter.
'watch' becomes 'view' (synonyms).
'view' with its final letter taken off is 'VIE'.
(Other definitions for vie that I've seen before include "Jockey" , "contest" , "I've got to contend" , "Engage in rivalry" , "Contend for superiority" .)