Mul"lion (?), n. [A corruption of munnion, F. moignon stump of an amputated limb, stump, OF. moing mutilated; cf. Armor. moñ, mouñ, mank, monk, and also L. mancus maimed.] (Arch.) (a) A slender bar or pier which forms the division between the lights of windows, screens, etc. (b) An upright member of a framing. See Stile.

Mul"lion, v. t. To furnish with mullions; to divide by mullions.