Jetty contains single colonist (7)
I believe the answer is:
pioneer
'colonist' is the definition.
(pioneer is a kind of colonist)
'jetty contains single' is the wordplay.
'jetty' becomes 'pier' (I've seen this before).
'contains' indicates putting letters inside.
'single' becomes 'one' (I've seen this before).
'pier' enclosing 'one' is 'PIONEER'.
(Other definitions for pioneer that I've seen before include "Innovate" , "One who blazes the trail for others" , "Innovator; first settler" , "make the first move!" , "Original developer" .)