Try very hard (4,1,3)
'try very hard' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bust a gut that I've seen before include "Really work extra hard" , "meet qualification for intestinal surgery?" , "Make a strenuous effort" , "Strain" , "Work extra hard to achieve something" .)
'try very hard' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for strive that I've seen before include "Make effort using rivets" , "Try extremely hard" , "Try hard to break rivets" , "Make a great effort" , "Vie; compete" .)