impertinent :: insolent
impervious :: not penetrable; not permitting passage through
impetuous :: violent; hasty; rash
impious :: irreverent
implacable :: incapable of being pacified
implicit :: understood but not stated
impolitic :: not wise
impregnable :: invulnerable
impromptu :: without previous preparation
improvident :: thriftless
inalienable :: not to be taken away; nontransferable
inane :: silly; senseless
inanimate :: lifeless
inarticulate :: speechless; producing indistinct speech
incarnate :: endowed with flesh; personified
incessant :: uninterrupted
inchoate :: recently begun; rudimentary; elementary
incipient :: beginning; in an early stage
incisive :: cutting; sharp
inclement :: stormy; unkind
inclusive :: tending to include all
incognito :: with identity concealed; using an assumed name
incommodious :: not spacious
incompatible :: inharmonious
inconsequential :: of trifling significance
incontrovertible :: indisputable
incorporeal :: immaterial; without a material body
incorrigible :: uncorrectable
indefatigable :: tireless
indigenous :: native
indigent :: poor
indisputable :: too certain to be disputed
indomitable :: unconquerable
indubitably :: beyond a doubt
indulgent :: humoring; yielding; lenient
ineffable :: unutterable; cannot be expressed in speech
inept :: unsuited; absurd; incompetent
inexorable :: relentless; unyielding; implacable
infallible :: unerring
infamous :: notoriously bad
infinitesimal :: very small
inflated :: enlarged with air or gas
ingenuous :: naive; young; unsophisticated
inherent :: firmly established by nature or habit
inimical :: unfriendly; hostile
iniquitous :: unjust; wicked
innate :: inborn
innocuous :: harmless
inordinate :: unrestrained; excessive
insatiable :: not easily satisfied; greedy
inscrutable :: incomprehensible; not to be discovered
insensate :: without feeling
insidious :: treacherous; stealthy; sly
insipid :: tasteless; dull
insolent :: haughty and contemptuous
insular :: like an island; narrow-minded
insuperable :: insurmountable; invincible
insurgent :: rebellious
interminable :: endless
intermittent :: periodic; on and off
intransigent :: refusing any compromise
intrepid :: fearless
intrinsic :: belonging to a thing in itself; inherent