How many letters does the top answer for “the act of colonizing; the establishment of colonies” have?

The most common answer is colonisation (12 letters).

Crossword clue: the act of colonizing; the establishment of colonies

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

colonisation 12 letters wn-def

the act of colonizing; the establishment of colonies

colonization 12 letters wn-def

the act of colonizing; the establishment of colonies