Pioneer? Hoskins is one, foremost of liars admitted! (7)
I believe the answer is:
settler
'pioneer?' is the definition.
(pioneer is a kind of settler)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for settler that I've seen before include "decisive blow" , "Coloniser - arbitrator" , "Colonist, pioneer" , "Person who moves into an uninhabited country" , "Early mover into an area" .)