from The American Heritage® Dictionary of the English Language, 4th Edition
- Large: megadose.
- Surpassing other examples of its kind; extraordinary: megahit.
- One million (106): megahertz.
- 1,048,576 (220): megabyte.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- Very large, great. Denoting a size larger than usual.
- In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by one million (106.) SI Symbol: M, computing abbreviation: Mi.
- Multiplying the unit to which it is attached by 220 (= 1,048,576, the binary round number closest to a million).
- Multiplying the unit to which it is attached by 210 × 103 (= 1024,000, the binary round number closest to thousand).
Greek, from megas, great; see meg- in Indo-European roots.(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek μέγας (megas, "great, large, mighty"), from Proto-Indo-European *meg- (“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. (Wiktionary)