mega- Mega- and its companion megalo-, both from Greek megas ‘great’, were already combining forms in ancient Greek, but were not used for forming new words in English until the middle of the 19th century. Since then they have been very prolific, producing mainly scientific words such as megabyte [M20th], megalithic [M19th] for the culture that built with monoliths (see lithograph), and megalomaniac [L19th], but also more informal words such as megastar [M20th] or megabucks [M20th] for a very large sum of money. Mega as a stand-alone term for ‘huge, very’ or as a term of approval is also mid 20th century.