impenetrability

noun 0.855

impregnability

noun 0.716

imperviousness

noun 0.698

impermeability

noun 0.669

penetrability

noun 0.654

inaccessible

noun 0.641

imperforate

noun 0.609

inscrutable

noun 0.603

impassibility

noun 0.600

impenitent

noun 0.594

penetrator

noun 0.593

unbreakable

noun 0.585

incomprehensible

noun 0.581

penetratin

noun 0.579

inaccessibility

noun 0.571

impenitence

noun 0.571

impossible

noun 0.567

incapable

noun 0.567

undoable

noun 0.567

invincible

noun 0.566

inscrutability

noun 0.563

unapproachability

noun 0.560

insoluble

noun 0.558

impasse

noun 0.557

unassailable

noun 0.556

unreachable

noun 0.552

immovable

noun 0.552

undatable

noun 0.551

unobtainable

noun 0.551

incombustible

noun 0.550

untranslatable

noun 0.549

imponderable

noun 0.547

incompressibility

noun 0.546

incomprehensibility

noun 0.545

indiscernible

noun 0.541

incorruptible

noun 0.540

imped

noun 0.539

impalement

noun 0.538

unattainable

noun 0.537

unanswerable

noun 0.536

intransigent

noun 0.535

insusceptibility

noun 0.534

undefeatable

noun 0.532

immeasurable

noun 0.532

implacability

noun 0.531

indecipherability

noun 0.525

inexorability

noun 0.523

incomprehension

noun 0.522

untranslatability

noun 0.521

impossibility

noun 0.521

opaque

noun 0.519

untouchable

noun 0.518

imperceptibility

noun 0.518

imperishable

noun 0.517

invincibility

noun 0.516

impediment

noun 0.514

unprintable

noun 0.513

intractability

noun 0.513

indestructibility

noun 0.511

inseparable

noun 0.511

opaqueness

noun 0.511

incomparable

noun 0.511

inviolability

noun 0.509

indefinable

noun 0.509

inimitability

noun 0.507

invulnerability

noun 0.507

unteachable

noun 0.507

inconceivability

noun 0.506

indigestible

noun 0.504

tough nut to crack

noun 0.502

infallible

noun 0.500

impeccability

noun 0.500