Wiktionary
oxonium
n. (context inorganic chemistry English) Any univalent oxygen cation derived from water, the simplest of which is the hydronium ion (H3O+).
Wikipedia
Usage examples of "oxonium".
When you handed Hatch an uncompleted cheque made out to Oxo for him to sign in that off-handed and very unbusinesslike way that he probably imagined was appropriate to being rich, was it not with the clear intention of expanding ‘Oxo’ to Oxonia, adding the rest of the firm’s title and finally inserting the amount—a substantial amount—for payment?