v.
- lose or cause to lose lustre, especially as a result of exposure to air or moisture.
- make less valuable or respected:
they make up negative stories to tarnish my image.
n.
loss of brightness.
▸a film or stain formed on an exposed surface of a mineral or metal.
Derivative
Etymology
ME: from Fr. terniss-, lengthened stem of ternir, from terne ‘dark, dull’.