Definition from Wiktionary, the free dictionary
Etymology 1 
smudge (plural smudges)
a blemish; a smear
Etymology 2 
From Middle English smogen.
- To obscure by blurring; to smear.
- To soil or smear with dirt.
- To use dense smoke to protect from insects.
- To stifle or smother with smoke.
- (paganism) To burn herbs as a cleansing ritual.
- (to obscure by blurring): blur, smear
- (to soil or smear with dirt): smutch, soil
- (to use smoke against insects): fumigate
to obscure by blurring
to soil or smear with dirt