Idiosyncrasy
Quirk, peculiarity
Ignominy
Shame or humiliation
Immutable
Not changing
Imperious
Arrogant, domineering
Implacable
Relentless, merciless
Impotent
Powerless
Impregnable
Invincible
Impromptu
Spontaneous
Impunity
Responsibility, absence of guilt
Incendiary
Flammable, heated
Inception
Beginning
Indigenous
Native
Inexorable
Unstoppable
Influx
Entry, arrival
Ingratiate
To grovel, to ‘suck up to’
Inhibition
Reserve, self-conscience
Innocuous
Harmless
Inordinate
Excessive
Insatiable
Unquenchable, voracious
Iconoclast
One who always finds faults