In English, the prefixes in and un, along with others, are used to negate certain root words. The antonym of sane, for example, is insane, and the antonym of stoppable, for example, is unstoppable. But some words that appear to be negated with prefixes have no positive. The opposite of inept is not ept -- there is no such word. Words With No Positive Forms debunk

defenestrate

dejected

disconsolate

disdain

disgruntled

dishevelled

dismayed

disrupt

feckless

gormless

impetuous

impromptu

inane incessant

inchoate

incognito

incommunicado

indomitable

ineffable

inept

inert

infernal

inhibited

insidious

insipid

insouciant

intact invert

misgivings

misnomer

nonchalant

noncommittal

nondescript

nonpareil

nonplussed

unbeknownst

ungainly

unswerving

untold

untoward Words With Uncommon Positive Forms The following words do have positives, formed by removing the negating prefix, but the positive forms of these words are far less common: disarray

disconcerting

immaculate

impeccable

inadvertent

incapacitated

incorrigible

inevitable innocent

inscrutable

insensate

insufferable

interminable

unbridled

unflappable unfurl

unkempt

unmitigated

unrequited

unruly

unthinkable

unwieldy

Suffixes

Sometimes antonyms are formed by appending the suffixes -ful and -less onto English words, as with joyful and joyless. But sometimes one is an English word and the other isn't. For example, reckless is an English word, and reckful is not. Other times, one is more commonly used than the other: ruthless and ruthful are both legitimate English words, but the former is used far more frequently than the latter.

Special Cases

An interesting special case is indefatigable, whose antonym is not defatigable but rather fatigable.

The antonym of the verb incline is disincline, which is arguably not a double negative but in any case looks like one.

The word inflammable is another interesting special case. Stripping off the prefix does not create an antonym but rather a synonym: flammable. This idiosyncrasy of English seems insidious (!) until one realizes that the prefix in- means something else in this case. The word inflammable means "able to be inflamed." Now it makes sense, doesn't it?