Opener I rearranged for colonist (7)
I believe the answer is:
pioneer
'for colonist' is the definition.
(pioneer is a kind of colonist)
'opener i rearranged' is the wordplay.
'rearranged' indicates anagramming the letters.
'opener'+'i'='openeri'
'openeri' with letters rearranged gives 'PIONEER'.
(Other definitions for pioneer that I've seen before include "Innovator; first settler" , "Innovator; early settler" , "First to explore a new area" , "spacecraft" , "Founder" .)