staining

verb
  1. 1

    To discolour.

    โ€œarmour stained with bloodโ€

  2. 2

    To taint or tarnish someone's character or reputation

  3. 3

    To coat a surface with a stain

    โ€œthe stained glass used for church windowsโ€

  4. 4

    To become stained; to take a stain.

  5. 5

    To treat (a microscopic specimen) with a dye, especially one that dyes specific features

  6. 6

    To cause to seem inferior or soiled by comparison.

Source: https://en.wiktionary.org/wiki/stain, https://en.wiktionary.org/wiki/staining