WordNet sense 1 (innermost or essential):

intimate, intimate

WordNet sense 2 (belonging to a thing by its very nature):

intrinsic, intrinsical

WordNet sense 3 (occurring within an institution or community):

intragroup

WordNet sense 4 (carried on within the bounds of an institution or community):

intramural

WordNet sense 5 (inside the country):

home, national

WordNet sense 6 (of concern to or concerning the internal affairs of a nation):

domestic

WordNet sense 7 (relating to or existing in the mind or thoughts):

inward

WordNet sense 8 (inside and toward a center):

interior

WordNet sense 9 (inside or closer to the inside of the body):

inner