Make a great effort (mental or physical) (5)
I believe the answer is:
exert
(Other definitions for exert that I've seen before include "Exercise, wield" , "Wield - apply" , "Act upon" , "Apply (pressure)" , "Expend" .)
I believe the answer is:
exert
(Other definitions for exert that I've seen before include "Exercise, wield" , "Wield - apply" , "Act upon" , "Apply (pressure)" , "Expend" .)