Swallow departs with every other one going west (3)
I believe the answer is:
eat
'swallow' is the definition.
(swallow can mean to consume or eat up)
'departs with every other one going west' is the wordplay.
'with every other one going west' means one should take alternating letters (to go west is to be killed or get lost).
The alternating letters of 'departs' are 'EAT'.
(Other definitions for eat that I've seen before include "Consume for tea" , "Be corrosive" , "Munch" , "Dine in a restaurant" , "Use a knife and fork" .)