Letter spelled out change in direction, largely (3)
I believe the answer is:
vee
'letter spelled out' is the definition.
(the spelled out name for the letter V)
'change in direction largely' is the wordplay.
'change in direction' becomes 'veer'.
'largely' means to remove the last letter.
'veer' with its last letter removed is 'VEE'.
(Other definitions for vee that I've seen before include "Angled mark or notch" , "Shape resembling the twenty-second letter" , "Character" , "Letter; notch shape" , "22nd letter of the alphabet" .)