Mar, n. — Webster enters it under “mar”
A small lake. See Mere. [Prov. Eng.]
2 other Webster entries under this spelling
Mar, v. t. [imp. & p. p. Marred (märd); p. pr. & vb. n. Marring.]
1. To make defective; to do injury to, esp. by cutting off or defacing a part; to impair; to disfigure; to deface. I pray you mar no more trees with wiring love songs in their barks. Shak. But mirth is marred, and the good cheer is lost. Dryden. Ire, envy, and despair Which marred all his borrowed visage. Milton.
2. To spoil; to ruin. "It makes us, or it mars us." "Striving to mend, to mar the subject." Shak.
Mar, n.
A mark or blemish made by bruising, scratching, or the like; a disfigurement.
Shades of meaning
Fernald lists marred only as an antonym, under perfect.
He lists it without comment; the entries above explain its neighbors.