1 immutable – changeless, invariable, unalterable, unchanging, undeviating
alterable, changing, inconsistent, vacillatory, varying
2 impervious – impassable, impenetrable, impermeable, inaccessible
accessible, enterable, passable, penetrable, perforable, porous
3 implacable - grim, merciless, relentless, unappeasable, unpacifiable, unrelenting
appeasable, clement, compassionate, conciliatory, merciful, reconcilable
4 incongruous – discordant, discrepant, incompatible, inconsistent, inconstant, uncongenial
appropriate, compatible, congruous, consistent, fitting, suitable
5 indolent – lazy, otiose, slothful, unindustrious,
assiduous, busy, diligent, industrious, sedulous
6 infallible – flawless, impeccable, inerrable, inerrant, unerring
errable, errant, fallible, imperfect
7 infirm – decrepit, frail, inconstant, irresolute, vacillating,
hale, healthy, vigorous, resolute, steadfast unwavering
8 innocuous – innocent, inoffensive, unoffending
harmful, pernicious
9 insatiate – gluttonous, unappeasable, unquenchable, unsated, unsatisfied
gratified, quenched, sated, satisfied, sufficed
10 inscrutable – arcane, impenetrable, inexplicable, mysterious, unknowable
comprehensible, intelligible, penetrable, perceivable, perspicuous
11 insensate – callous, dispassionate, insensitive, unaffected, unfeeling, unmoved
compassionate, empathetic, responsive, sensitive, tender-hearted
12 irrelevant – extraneous, immaterial, inapplicable, inconsequent, unconnected, unrelated
applicable, germane, pertaining, pertinent, related