Mega/Megabucks etc

Mega- as a prefix (meg- before a vowel) derives from the Ancient Greek mega meaning great or large. As a prefix measuring large units its usage dates back many years, exactly how many years, depends on the word that is prefixed. For example, megacosm, any large or complex entity, dates from the early 1600s, whereas megawatt, a million watts, dates from the early 20th century. Mega today has three meanings. Its scientific meaning as a unit prefix of measurement is one million of anything e.g. megahertz, megapixel, megabyte etc. Its second meaning, qualifying absolutely anything e.g. megaflop, megahit, megajoke, etc simply indicates great size or extent. For example, megabucks is American slang that means lots of money and dates from the late 1940s. Finally, as a word on its own, its simply means very big or lots of anything, and this usage is first cited from the early 1980s.