word-forming element meaning "long, abnormally large, on a large scale," taken into English via French and Medieval Latin from Greek makros "long, large," from PIE root *mak- "long, thin."

word-forming element meaning "magnetic, magnetism," from Greek magneto-, combining form of magnes (see magnet).

word-forming element of Latin origin meaning "bad, badly, ill, poorly, wrong, wrongly," from French mal (adv.), from Old French mal (adj., adv.) "evil, ill, wrong, wrongly" (9c.), from Latin male (adv.) "badly," or malus (adj.) "bad, evil" (fem. mala, neuter malum), from Proto-Italic *malo-, from PIE *mol-o-, probably from PIE root *mel- (3) "false, bad, wrong."

Most Modern English words with this element are 19c. coinages. It generally implies imperfection or deficiency, but often it is simply negative (as in malfeasance, malcontent). It is equivalent to dys- and caco- of Greek origin and Germanic mis- (1).

word-forming element meaning "breast," from Latin mamma "breast" (which is cognate with mamma). The form mammato-, used in cloud terminology in reference to smooth, rounded shapes, is from Latin mammatus.

before vowels mast-, word-forming element meaning "female breast, mammary gland," from Greek mastos "woman's breast," from madan "to be wet, to flow," from PIE *mad- "wet, moist, dripping" (source also of Latin madere "be moist;" Albanian mend "suckle;" see mast (n.2)).

combining form meaning "mother," from Latin māter (see mother (n.1)).

before vowels meg-, word-forming element often meaning "large, great," but in physics a precise measurement to denote the unit taken a million times (megaton, megawatt, etc.), from Greek megas "great, large, vast, big, high, tall; mighty, important" (fem. megale), from PIE root *meg- "great." Mega began to be used alone as an adjective by 1982.

High-speed computer stores 2.5 megabits [headline in "Electronics" magazine, Oct. 1, 1957]

before vowels mer-, word-forming element meaning "part, partial, fraction," from Greek meros "a part, a fraction," from PIE root *(s)mer- (2) "to get a share of something."

before vowels mes-, word-forming element meaning "middle, intermediate, halfway," from Greek mesos "middle, in the middle; middling, moderate; between" (from PIE root *medhyo- "middle").

word-forming element of Greek origin meaning 1. "after, behind; among, between," 2. "changed, altered," 3. "higher, beyond;" from Greek meta (prep.) "in the midst of; in common with; by means of; between; in pursuit or quest of; after, next after, behind," in compounds most often meaning "change" of place, condition, etc. This is from PIE *me- "in the middle" (source also of German mit, Gothic miþ, Old English mið "with, together with, among").

The notion of "changing places with" probably led to the senses of "change of place, order, or nature," which was a principal meaning of the Greek word when used as a prefix (but it also denoted "community, participation; in common with; pursuing").

The third, modern, sense, "higher than, transcending, overarching, dealing with the most fundamental matters of," is due to misinterpretation of metaphysics (q.v.) as "science of that which transcends the physical." This has led to a prodigious erroneous extension in modern usage, with meta- affixed to the names of other sciences and disciplines, especially in the academic jargon of literary criticism: Metalanguage (1936) "a language which supplies terms for the analysis of an 'object' language;" metalinguistics (by 1949); metahistory (1957), metacommunication, etc.