Antidote

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late Middle English: via Latin, from Greek antidoton, neuter of antidotos ‘given against’, from anti- ‘against’ + didonai ‘give’.

wiktionary

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From Latin antidotum, from Ancient Greek ἀντίδοτον(antídoton), neuter of ἀντίδοτος(antídotos, “given as a remedy for”), from ἀντιδίδωμι(antidídōmi, “I give in return, repay”), from ἀντί(antí, “against”) + δίδωμι(dídōmi, “I give”). Compare French antidote.

etymonline

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antidote (n.)

"remedy counteracting poison," early 15c. (c. 1400 as antidotum), from Old French antidot and directly from Latin antidotum/antidotus "a remedy against poison," from Greek antidoton (pharmakon) "(drug) given as a remedy," from antidoton literally "given against," verbal adjective of antididonai "give for" (also "give in return, give instead of") from anti "against" (see anti-) + didonai "to give" (from PIE root *do- "to give"). Compare Middle English antidotarie "treatise on drugs or medicines" (c. 1400).