Mimation refers to the suffixed -m (the letter mem in many Semitic abjads) which occurs in some Semitic languages.
This occurs in Akkadian on singular nouns. It was also present in the Proto-Semitic language.
It is retained in the plural and the few remaining dual forms in Modern Hebrew. It corresponds to the letter nun (-n) in Classical Arabic and is retained in the singular (nunation), dual, and plural.
References
Mimation Wikipedia(Text) CC BY-SA