Definition of oxonium in US English:

oxonium

noun

Chemistry
  • The hydroxonium ion, H₃O+; any analogue of this in which one or more of the hydrogen atoms are replaced by organic groups. Usually attributive.

Origin

Late 19th century. From oxy- + -onium.

Pronunciation

oxonium

/ɒkˈsəʊnɪəm/