To soil, stain, or dirty with or as if with a smearing agent: "their tough, hostile faces, smirched by the grime and rust” ( Henry Roth).
To dishonor; defame.
Something, such as a blot, smear, or stain, that smirches.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.