Webster's Revised Unabridged Dictionary · 1913

Tarnish

Tarnish , transitive verb

[French ternir, from Old High German tarnen to darken, to conceal, hide; akin to Old Saxon dernian to hide, Anglo-Saxon dernan, dyrnan, Old High German tarni hidden, Old Saxon derni, Anglo-Saxon derne, dyrne. Compare Dern, a., and see -ish.]

To soil, or change the appearance of, especially by an alternation induced by the air, or by dust, or the like; to diminish, dull, or destroy the luster of; to sully; as, to tarnish a metal; to tarnish gilding; to tarnish the purity of color.
Tarnished lace. — Fuller

Tarnish , intransitive verb

To lose luster; to become dull; as, gilding will tarnish in a foul air.
Till thy fresh glories, which now shine so bright, Grow stale and tarnish with our daily sight. — Dryden

Tarnish , noun

1.
The quality or state of being tarnished; stain; soil; blemish.
2.
(Mineralogy) A thin film on the surface of a metal, usually due to a slight alteration of the original color; as, the steel tarnish in columbite.