Inimitable
One of a kind, peerless
His inimitable feats of daring on the trapeze were so audacious that no one else even tried to imitate them
Iniquity
Wickedness, gross injustice
The iniquity of the judgement was so blatant that there was immediate worldwide protest of its unfairness
*iniquitous means characterized by wickedness
Injudicious
Showing lack of judgement, unwise, imprudent, indiscreet
She was an injudicious in his handling of the affair that the situation soon turned into a disaster
Innervate
To supply with nerves, energize
Innervated by our coach’s pep talk, we were filled with energy for the upcoming game
Innocuous
Harmless; causing no damage
The poison-looking brew turned out to be innocuous; it didn’t taste very good, but it didn’t cause any harm
Inscrutable
Incapable of being discovered or understood; mysterious
Quantum mechanics is inscrutable to me, so I’ve given up even trying to understand it
Insensible
Unconscious, unresponsive, unaware, unaffected, numb
I am not insensible of your suffering; I just don’t care
Insipid
Without taste or flavor, lacking in spirit or dull
Henry’s sense of humor was so insipid that he thought all knock-knock jokes were funny
Insouciant
Unconcerned, carefree, nonchalant
Her insouciant attitude toward her schoolwork means that she rarely turned in her papers or bothered to study for a test
Insular
Parochial, narrow minded, like an island
The insularity of his upbringing was reflected in the narrow mindedness of his views
Inimical
Damaging, harmful, injurious, hostile, unfriendly; pernicious
He seemed inimical to my overtones of friendship, refusing even to talk to me