Stick-to-itiveness
'stick-to-itiveness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for grit that I've seen before include "Persevering courage" , "Gravel or colloquial courage" , "Determination - small bits of stone" , "Grains of rock or sand" , "Courage; tiny stones" .)
(Other definitions for zeal that I've seen before include "Laze about with energy" , "Fervent devotion" , "Great eagerness" , "Extreme enthusiasm" , "Zing" .)
(Other definitions for will that I've seen before include "Volition" , "Intention, desire" , "mind" , "- And Grace, TV series" , "Inclination" .)