antimatter n.

word-forming element of Greek origin meaning "against, opposed to, opposite of, instead," shortened to ant- before vowels and -h-, from Old French anti- and directly from Latin anti-, from Greek anti (prep.) "over, against, opposite; instead, in the place of; as good as; at the price of; for the sake of; compared with; in opposition to; in return; counter-," from PIE *anti "against," also "in front of, before" (from root *ant- "front, forehead," with derivatives meaning "in front of, before"), which became anti- in Italian (hence antipasto) and French.

It is cognate with Sanskrit anti "over, against," and Old English and- (the first element in answer). A common compounding element in Greek, in some combinations it became anth- for euphonic reasons. It appears in some words in Middle English but was not commonly used in English word formations until modern times. In a few English words (anticipate, antique) it represents Latin ante.

In noun compounds where it has the sense of "opposed to, opposite" (Antichrist, anti-communist) the accent remains on the anti-; in adjectives where it retains its old prepositional sense "against, opposed to," the accent remains on the other element (anti-Christian, anti-slavery).

c. 1200, materie, "the subject of a mental act or a course of thought, speech, or expression," from Anglo-French matere, Old French matere "subject, theme, topic; substance, content; character, education" (12c., Modern French matière) and directly from Latin materia "substance from which something is made," also "hard inner wood of a tree." According to de Vaan and Watkins, this is from mater "origin, source, mother" (see mother (n.1)). The sense developed and expanded in Latin in philosophy by influence of Greek hylē (see hylo-) "wood, firewood," in a general sense "material," used by Aristotle for "matter" in the philosophical sense. 

The Latin word also is the source of Spanish, Portuguese, and Italian materia, Dutch, German, and Danish materie, vernacular Spanish madera, Portuguese madeira "wood" (compare Madeira). The Middle English word also sometimes was used specifically as "piece of wood."

From c. 1200 as "a subject of a literary work, content of what is written, main theme;" sense of "narrative, tale, story" is from c. 1300. Meaning "physical substance generally" is from mid-14c.; that of "substance of which some specific object is or may be composed" is attested from late 14c. Meaning "piece of business, affair, activity, situation; subject of debate or controversy, question under discussion" is from late 14c. In law, "something which is to be tried or proved," 1530s.

Matter of course "something expected" attested from 1739 (adjectival phrase matter-of-course "proceeding as a natural consequence" is by 1840). For that matter "as far as that goes, as far as that is concerned" is attested from 1670s. What is the matter "what concerns (someone), what is the cause of the difficulty" is attested from mid-15c., from matter in the sense of "circumstance or condition as affecting persons and things." To make no matter to "be no difference to" also is mid-15c., with matter in the meaning "importance, consequence."