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Mega- is a combining form used like a prefix meaning “large, great, grand, abnormally large.” It is used in many scientific and medical terms.

In science, mega- is specifically used as a prefix in units of measure equaling a factor of “one million.” It’s abbreviation is M. So, a megawatt (MW) is one million watts.

Mega- comes from the Greek ��é������, meaning “large” or “great.”

What are variants of mega-?

When combined with words or word elements that begin with a vowel, mega- becomes meg-, as in megohm.

Mega- is a variant of megalo- and megal-, as in megalomania and megalopsia. Learn more about their specific applications in our 51�Թ�s That Use articles.

A word you may have encountered that features the combining form mega- is megalith, “a stone of great size, especially in ancient construction work, as the Cyclopean masonry, or in prehistoric Neolithic remains, as dolmens or menhirs.” Some of the most well-known megaliths in the world can be found at Stonehenge.

The mega- part of the word means “large,” as we know. The second part of the word, -lith, means “stone,” from the Greek ��í�ٳ�Dz�. Megalith literally translates to “large stone.”

What are some words that use the combining form mega-?

• megabacterium
• megabit
• megabyte
• megacephaly
• megachurch
• megacity
• megadeath
• megadont
• megaesophagus
• megafauna
• megaflop
• megagamete
• megahertz
• megahit
• megajoule
• megakaryocyte
• megalitre
• megapixel
• megaplex
• megaphyll
• megaparsec
• megapolis
• megascopic
• megasporangium
• megastructure
• megaton
• megavolt

What are some other forms that mega- may be commonly confused with?

• macro-
• neg-

Not every word that begins with the exact letters mega- or meg- is necessarily using the combining form mega- to denote “large,” e.g., megillah, megilp, or megass. Learn where these words come from and what they mean at our entries.

The combining form -phyll means “leaf.” What does megaphyll, which ferns and seed plants produce, literally translate to?