Mansard - A roof type with two slopes on each of the four sides, the lower slope being steeper than the other; capped off with a cupola, typically Victorian.

Masonry - Stonework or brickwork

Meeting Rails - The name applied to rails of window sash that meet one another when the window is closed.

Millwork - Finished woodwork, cabinetry, carving, etc.

Modillion - A bracket supporting the upper part of a composite or Corinthian cornice.

Modular Planning - Planning a home in multiples of four feet in order to reduce material waste and cut labor cost.

Molding - Shaped decorative outlines on projecting cornices and members in wood and stone.

Mullion - The vertical member separating adjacent windows.

Muntin - Wood or metal strips separating lites.