[tar.nish] vb [MF terniss-, stem of ternir, prob. of Gmc origin; akin to OHG ternen to hide] vt (1598) 1: to dull or destroy the luster of by or as if by air, dust, or dirt: soil, stain
2. a: to detract from the good quality of: vitiate "his fine dreams now slightly ~ed" b: to bring disgrace on: sully ~ vi: to become tarnished -- tar.nish.able adj
[2]tarnish n (1713): something that tarnishes; esp: a film of chemically altered material on the surface of a metal (as silver)