To smirch or soil; to discolor; to obscure. Hence: To dishonor; to sully.

ETYM Old Eng. defoulen, -foilen, to tread down, Old Fren. defouler; de- + fouler to trample, and Old Eng. defoulen to foul (influenced in form by the older verb defoilen). Related to File to defile, Foul, Defoul.
To place under suspicion or cast doubt upon; SYN. sully, corrupt, taint, cloud.

To make soiled, filthy, or dirty; SYN. soil, begrime, grime, colly, bemire.

ETYM Old Eng. soilen, Old Fren. soillier, French souiller, (assumed) Late Lat. suculare, from Latin sucula a little pig, dim. of sus a swine. Related to Sow.
1. To make dirty or unclean on the surface; to foul; to dirty.
2. To stain or mar, as with infamy or disgrace; to tarnish.

To soil; to make dirty; to spot; to tarnish