Substance symbolized by a skull and crossbones (6)

I believe the answer is:

poison

(Other definitions for poison that I've seen before include "[ADDER] 's defence" , "Eg, strychnine" , "Venom, harmful substance" , "It causes illness or death in a living organism" , "Substance that damages tissues or causes death" .)

I've seen this clue in the USA Today.

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