The "M" in MVP (4)
I believe the answer is:
most
'the m in mvp' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for most that I've seen before include "Nearly all, majority" , "Extremely, very" , "Kind of commercial pact where two countries agree to treat each other as well as any other" , "Greatest in amount or degree" , "Almost all" .)