— cryptic
— cryptical
— deep
— in spite of
— incapable
— incapacitate
— incipience
— incipient
— incomprehensible
— inescapable
— inexpedient
— inexpensive
— inexpensively
— inexperience
— inexperienced
— inexpert
— inexpressible
— inscrutable
— insoluble
— inspector
— inspiration
— inspire
— inspired
— inspiring
— insufferable
— insuperable
— mysterious
— mystifying
— paradoxical
— self-contradictory
— unaccountable
— uncomprehensible
— unexplainable
— unexplained