Definition of "hydrogen ion"

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

(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  examples

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