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.
"small, square single-colored display elements that comprise an image," 1969, coined to describe the photographic elements of a television image, from pix + first syllable of element.