The Collaborative International Dictionary
Megalo-
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.
Megalo-
Megalo- \Meg"a*lo-\ See Meg-.
Douglas Harper's Etymology Dictionary
megalo-
word-forming element meaning "large, great, exaggerated," from comb. form of Greek megas "large, great" (stem megal-); see mickle.
Wiktionary
megalo-
pre. large, great or exaggerated