Grammatically Correct: The writer's essential guide to punctuation ...

Negative Formations
Unreliable. Irreversible. Disloyal. Indecisive. Impractical.
Atypical. Counterintuitive. Illiterate. Abnormal. Deactivate.
Misremember. Antiracism. Nonaddictive. Maladjusted. Childless.
Cholesterol-free. Just as not every plural is formed by adding
s to the singular, not every negative is formed by adding un. One
of the challenges of the English language is the variety of addons
that can be united with base words to create their opposites.
Sometimes the reason for using a given prefix or suffix has to do
with the meaning of the negative word, sometimes with the form
or the etymological root of the base word. The result of all this
variation is that negative words present yet another pitfall to the
unwary writer, and are the source of many common errors.
Varied as they are, negative prefixes and suffixes aren't utterly
arbitrary. Their specific meanings are as follows:
A-OR AN-
(an before a vowel or the letter h)
Without, lacking, absent achromatic, asexual, amoral,
ANTI­
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anaerobic, anhedonia
Opposite of antimatter, Antichrist, anti­
clockwise (alternative to
counterclockwise)
Preventing or alleviating antidepressant, antifreeze
Combating or defending against antimissile, antiaircraft, antibiotic
Opposed to or hostile to antimonarchist, antivivisectionist,
anti-Semitic