hydrogen ion

(chemistry) Used other than figuratively or idiomatically: see hydrogen, ion. ; H⁻ or H⁺

(chemistry) a proton combined with one or more water molecules; usually written H₃O⁺ and called the hydronium ion though is best considered as H₉O₄⁺ but is often written H⁺_((aq)) for simplicity

(chemistry) a bare hydrogen nucleus; a proton, deuteron or triton