Neckline shape (3)
I believe the answer is:
vee
'neckline shape' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for vee that I've seen before include "Letter; notch shape" , "Shape resembling the twenty-second letter" , "22nd letter of the alphabet" , "Character" , "Angled mark or notch" .)