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My- is a combining form used like a prefix meaning “muscle.” It is often used in medical terms, especially in anatomy.

My- comes from the Greek ��ŷ��, meaning “muscle” and “mouse.” Mouse? You read that right. Discover why at our entry for muscle!

My- is a variant of myo-, which loses its -o- when combined with words or word elements beginning with vowels. Want to know more? Read our �������t¶��s That Use myo– article.

An example of a word you may have seen that features my- ������myatonia, meaning “deficient muscle tone.”

We know my- means “muscle.” What about –atonia? It’s based on atonia (also atony), “lack of tone or energy.” Myatonia, then, literally translates to “lack of muscle tone or energy.” Learn more about atonia at our entry for the word.

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

• myalgia
• myasthenia
• myatrophy

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

• myel-
• myelo-

Not every word that begins with the exact letters my- is necessarily using the combining form my- to denote “muscle,” e.g., myopic or myriad.

The noun asthenia means “lack or loss of strength; weakness.” With that in mind, what would a patient with myasthenia be experiencing?