blemish (v.) Look up blemish at
early 14c., "to hurt, damage," from Old French blemiss- "to turn pale," extended stem of blemir, blesmir "to make pale; stain, discolor," also "to injure" (13c., Modern French blêmir), probably from Frankish *blesmjan "to cause to turn pale," or some other Germanic source, from Proto-Germanic *blas "shining, white," from PIE root *bhel- (1) "to shine, flash, burn," also "shining white."

The order of appearance of senses in Middle English is "hurt, damage;" "impair morally, sully" (late 14c.); "mar, spoil, injure" (early 15c.); "mar the beauty or soundness of" (mid-15c.). Usually in reference to something that is well-formed or otherwise excellent. Related: Blemished; blemishing.
blemish (n.) Look up blemish at
"a defect, flaw, imperfection," 1520s, from blemish (v.).