IPA: /ˌkɒlənaɪˈzeɪʃənɪst/
KK: /ˌkɒlənaɪˈzeɪʃənɪst/
A person who supports or promotes the establishment of colonies in a new territory.
The colonizationist argued for the benefits of expanding the empire into new lands.
Colonizationist is formed from "colonize" (from Latin "colonia", meaning a settlement) and the suffix "-ist" (meaning a person who practices or is concerned with something). The term refers to a person who advocates for or engages in the act of establishing settlements in new territories.
Think of a 'settlement' ('colonia') and remember that a 'colonizationist' is someone who is involved in creating or supporting those settlements.