M vs molar concentration

M and molar concentration both are nouns.

Word	Noun	Adjective	Verb	Adverb
M	Yes	No	No	No
molar concentration	Yes	No	No	No

As nouns, M and molar concentration are synonyms defined as:

M and molar concentration: concentration measured by the number of moles of solute per liter of solution

Other synonyms of M include molarity.

M (noun)	molar concentration (noun)
concentration measured by the number of moles of solute per liter of solution	concentration measured by the number of moles of solute per liter of solution
the 13th letter of the Roman alphabet
the cardinal number that is the product of 10 and 100
a unit of information equal to 1024 kibibytes or 2^20 (1,048,576) bytes
a unit of information equal to 1000 kilobytes or 10^6 (1,000,000) bytes