WordNet sense 1 ((ecology) the process by which a plant or animal becomes established in a new habitat):

ecesis

WordNet sense 2 (the persons (or committees or departments etc.) who make up a body for the purpose of administering something):

administration, brass, governance, organization, organisation, governing body

WordNet sense 3 (an organization founded and united for a specific purpose):

institution

WordNet sense 4 (the cognitive process of establishing a valid proof):

validation

WordNet sense 5 (the act of forming something):

constitution, formation