MAN - An adult male human.
MAT - A flat piece of coarse material used for wiping one's feet, or as a decorative or protective floor covering.
MOO - The characteristic sound made by a cow or bull.
NOT - Negates the meaning of the modified verb.
TAN - A symbol of the trigonometric function tangent.
TON - A unit of weight (mass) equal to 2240 pounds (a long ton) or 2000 pounds (a short ton) or 1000 kilograms (a metric ton).
TOO - Likewise.
OAT - Widely cultivated cereal grass, typically Avena sativa.
ATOM - The smallest, indivisible constituent part or unit of something.
MOON - The largest satellite of Earth.
ONTO - Upon; on top of.
MOAN - A low, mournful cry of pain, sorrow or pleasure.
MOAT - A deep, wide defensive ditch, normally filled with water, surrounding a fortified habitation.
MONO - Short name for the disease mononucleosis.
MOOT - Subject to discussion (originally at a moot); arguable, debatable, unsolved or impossible to solve.
TOON - A cartoon, especially an animated television show.
TOOT - The noise of a horn or whistle.
MOTTO - A sentence, phrase, or word, forming part of an heraldic achievement.
TOMATO - A widely cultivated plant, Solanum lycopersicum, having edible fruit.
OTTOMAN - An upholstered sofa, without arms or a back, sometimes with a compartment for storing linen, etc.