Used manoeuvre to enter eastern sea (8)
I believe the answer is:
employed
'used' is the definition.
('employ' can be a synonym of 'use')
'manoeuvre to enter eastern sea' is the wordplay.
'manoeuvre' becomes 'ploy' (ploy is a kind of manoeuvre).
'to enter' indicates putting letters inside.
'eastern' becomes 'e'.
'sea' becomes 'med' (short for Mediterranean).
'e'+'med'='emed'
'ploy' placed into 'emed' is 'EMPLOYED'.
(Other definitions for employed that I've seen before include "Working" , "Gave work to" , "Engaged in paid work" , "Engaged - used" , "in a job" .)