Entry 1 sense Webster, 1913 Toxicologist /täkˌ-sĭk-äl'-əj-ĭst/ · Tox·i·col·o·gist · IPA /tˌɑksɪkˈɑlədʒɪst/ 01 n. One versed in toxicology; the writer of a treatise on poisons. 1. One versed in toxicology; the writer of a treatise on poisons.