Etymology Learned borrowing from Ancient Greek κᾰτῐόν (kătĭón), neuter present participle of κᾰ́τειμῐ (kắteimĭ, “to go down, come down”), from κᾰτᾰ- (kătă-, “downwards, down, cata-”) + εἶμῐ (eîmĭ, “to go, come”). Coined by English polymath William Whewell in 1834 for Michael Faraday, who introduced it later that year. By surface analysis, cat(a)- + ion.
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Chemistry, Natural sciences, Physical sciencesPhysical A positively charged ion: one that would be attracted to the cathode in electrolysis.