Meaning of “tarnish” - Learner’s Dictionary

tarnish

verb uk us /ˈtɑːnɪʃ/
SOMEONE [ T ]

to spoil the way in which people think of someone so that they do not respect them:

to tarnish someone's image/reputation
METAL [ I, T ]

If a metal tarnishes or something tarnishes it, it becomes less bright and shiny.

(Definition of “tarnish” from the Cambridge Learner’s Dictionary © Cambridge University Press)