Dictionary:

thimerosal

  (thī-mĕr'ə-săl')

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A cream-colored crystalline powder, C₉H₉HgNaO₂S, used as a local antiseptic for abrasions and minor cuts.

[THI(O)– + MER(CURY) + –O– + SAL(ICYLATE).]

A cream-colored crystalline powder used as a local antiseptic for abrasions and minor cuts.

The noun has one meaning:

Meaning #1: a light-colored crystalline powder (trade name Merthiolate) used as a surgical antiseptic
  Synonyms: sodium ethylmercurithiosalicylate, Merthiolate