Be first to leave? (5)
I believe the answer is:
start
I believe this is a triple definition!
'be' is the first definition.
(I know that start is a type of be)
'first' is the second definition.
(synonyms)
'to' acts as a link.
'leave?' is the third definition.
(starting is a kind of leaving)
(Other definitions for start that I've seen before include "launch" , "Origin" , "begin an argument?" , "Onset" , "Opening - jump" .)