- Icky
- Ignoble
- Ignominious
- Ignorant
- Ill
- Illegal
- Illegible
- Illegitimate
- Ill-equipped
- Ill-fated
- Ill-humored
- Ill-mannered
- Ill-natured
- Illogical
- Ill-prepared
- Ill-tempered
- Ill-treated
- Illusory
- Imbalanced
- Immaterial
- Immeasurable (in a bad way)
- Immobile
- Immoral
- Immovable
- Impaired
- Impatient
- Impeachable
- Impecunious
- Impersonal
- Impetuous
- Impish (in a troublesome way)
- Impolite
- Imposing (in an intimidating way)
- Impossible
- Impoverished
- Impractical
- Imprecise
- Impure
- Impulsive
- Impure
- Inaccessible
- Inaccurate
- Inactive
- Inadequate
- Inadmissible
- Inadvertent
- Inadvisable
- Inappropriate
- Inarticulate
- Inattentive
- Inauspicious
- Incapable
- Incendiary
- Incensed
- Incessant
- Incisive (in a cutting way)
- Incoherent
- Incompatible
- Incomplete
- Incomprehensible
- Inconceivable
- Inconclusive
- Incongruous
- Inconsequential
- Inconsiderate
- Inconsistent
- Inconsolable
- Inconvenient
- Incorrect
- Incorrigible
- Increasingly-worse
- Indecent
- Indecisive
- Indefensible
- Indefinite
- Indelicate
- Indifferent
- Indignant
- Indiscreet
- Indisposed
- Indistinct
- Indolent
- Indulgent (in a careless way)
- Ineffective
- Inefficient
- Inelegant
- Ineligible
- Ineloquent
- Inept
- Inescapable
- Inessential
- Inevitable (in a bad way)
- Inexact
- Inexcusable
- Inexperienced
- Inexplicable
- Inexpressive
- Infallible (in a sarcastic way)
- Inferior
- Infested
- Infinitesimal (in a useless way)
- Inflamed
- Inflammatory
- Inflated
- Infuriating
- Inhospitable
- Inhumane
- Inimical
- Injudicious
- Injurious
- Inmate-like
- Innate (in a limiting way)
- Inoperable
- Inopportune
- Inordinate
- Insane
- Insatiable
- Inscrutable
- Insecure
- Insensitive
- Insidious
- Insignificant
- Insipid
- Insolent
- Insufferable
- Insufficient
- Insulting
- Insurmountable
- Intemperate
- Intense (in an overwhelming way)
- Interfering
- Intimidating
- Intolerable
- Intolerant
- Intractable
- Intrusive
- Invalid
- Invasive
- Involuntary
- Irate
- Irascible
- Irksome
- Irreconcilable
- Irrecoverable
- Irredeemable
- Irrefutable (in a stubborn way)
- Irregular
- Irrelevant
- Irreparable
- Irresponsible
- Irreverent
- Irritable
- Irritating
- Isolated
- Itchy
