Colonist, one taking part in landing (7)
I believe the answer is:
pioneer
'colonist' is the definition.
(pioneer is a kind of colonist)
'one taking part in landing' is the wordplay.
'taking part in' indicates putting letters inside.
'landing' becomes 'pier' (pier is a kind of landing).
'one' inserted inside 'pier' is 'PIONEER'.
(Other definitions for pioneer that I've seen before include "Innovate" , "spacecraft" , "Innovator; early settler" , "Groundbreaker" , "Original developer" .)