LowerLeftArrow[x, y, ...] displays as x \[LowerLeftArrow] y \[LowerLeftArrow] ....
LowerRightArrow[x, y, ...] displays as x \[LowerRightArrow] y \[LowerRightArrow] ....
LyonsGroupLy[] represents the sporadic simple Lyons group Ly.
ManhattanDistance[u, v] gives the Manhattan or "city block" distance between vectors u and v.
Medium
(Built-in Mathematica Symbol) Medium is a style or option setting that specifies that objects should be medium sized.
MenuPacket[integer, string] is a MathLink packet indicating a menu request with title string.
MinusPlus[x] displays as \[MinusPlus]x.MinusPlus[x, y, ...] displays as x \[MinusPlus] y \[MinusPlus] ....
MonsterGroupM[] represents the sporadic simple monster group M.
MorphologicalBranchPoints[image] gives a version of a binary image image in which white pixels represent the morphological branch points.
Negative[x] gives True if x is a negative number.