The Collaborative International Dictionary
Meg-
Meg- \Meg-\ (m[e^]g-), Mega \Meg"a\ (m[e^]g"[.a]-), Megalo- \Meg"a*lo-\ (m[e^]g"[.a]*l[-o]-). [Gr. me`gas, gen. mega`loy, great.] Combining forms signifying:
Great, extended, powerful; as, megascope, megacosm.
(Metric System, Elec., Mech., etc.) A million times, a million of; as, megabyte, a million butes; megawatt, a million watts; megameter, a million meters; megafarad, a million farads; megohm, a million ohms.
Wiktionary
meg-
pre. Form of the SI prefix '''mega-''' used before a vowel, as in ''megohm''.