Why is the ninth month called September?
as a stand-alone word, attested from 1788, originally in reference to the anti-federalists in U.S. politics (in the 1830s, of the Anti-Masonic party); as an adjective, from 1857. From anti- in various usages.
word-forming element meaning "against, opposed to, opposite of, instead," from Old French anti- and directly from Latin anti-, from Greek anti "against, opposite, instead of," also used as a prefix, from PIE *anti "against," also "in front of" (see ante). It appears in some words in Middle English but was not commonly used in word formations until modern times.
anti- or ant-
Opposing; against: antisocial.
Counteracting; neutralizing: antibody.
A prefix whose basic meaning is "against." It is used to form adjectives that mean "counteracting" (such as antiseptic, preventing infection). It is also used to form nouns referring to substances that counteract other substances (such as antihistamine, a substance counteracting histamine), and nouns meaning "something that displays opposite, reverse, or inverse characteristics of something else" (such as anticyclone, a storm that circulates in the opposite direction from a cyclone). Before a vowel it becomes ant-, as in antacid.
A person opposed to a particular plan, position, action, etc: The vote showed three pros and six antis