Star mostly not eating dairy, meat, fish or eggs (4)
I believe the answer is:
vega
'star' is the definition.
(Vega is an example)
'mostly not eating dairy meat fish or eggs' is the wordplay.
'mostly' means to remove the last letter.
'not eating dairy meat fish or eggs' becomes 'vegan'.
'vegan' with its final letter removed is 'VEGA'.
(Other definitions for vega that I've seen before include "Bright star of constellation Lyra" , "Brightest star of constellation Lyra" , "First magnitude star" , "Gave turn to a star" , "Fifth brightest star" .)