Endeavour heading left a bit (6)
I believe the answer is:
morsel
'a bit' is the definition.
(I know that bit can be written as morsel)
'endeavour heading left' is the wordplay.
'endeavour' becomes 'morse' (I've seen this before).
'heading' is a charade indicator (letters next to each other) (some letters go in front of or head others).
'left' becomes 'l' (common abbreviation).
'morse'+'l'='MORSEL'
(Other definitions for morsel that I've seen before include "A tiny bit" , "Bite to eat" , "Small mouthful of food" , "A scrap or shred of food" , "Tiny piece" .)