Mega- Definition

megə

prefix

Large.

Megadose.

American Heritage

Surpassing other examples of its kind; extraordinary.

Megahit.

American Heritage

One million (10⁶ ).

Megahertz.

American Heritage

1,048,576 (2²⁰ ).

Megabyte.

American Heritage

(originally) Very large, great. Denoting a size larger than usual.

Wiktionary

adjective

Great in size, quantity, etc., often in relation to others of its kind.

Webster's New World

(informal) Very large.

Wiktionary

(slang, 1990s) Great; excellent.

Wiktionary

affix

Large, great, powerful.

Megacephalic, megaphone.

Webster's New World

Huge in size, number, etc.

A mega-yacht.

Webster's New World

To an enormous degree.

Mega-popular.

Webster's New World

One million; the factor 10⁶

Megahertz, megaton.

Webster's New World

Origin of Mega-

From Ancient Greek μέγας (megas, “great, large, mighty"), from Proto-Indo-European *meǵhâ‚‚s (“great"). Cognate with Latin magnus, and with Germanic words: Gothic 𐌼𐌹𐌺𐌹𐌻𐍃 (mikils), Old English micel, Middle English muchel, English much, Old High German mihhil, Old Norse mikill, Danish meget.

From Wiktionary
Greek from megas great meg- in Indo-European roots

From American Heritage Dictionary of the English Language, 5th Edition
Gr mega- < megas, great, mighty: see much

From Webster's New World College Dictionary, 5th Edition
From the prefix mega-.

From Wiktionary