phosphonium

A univalent cation, PH₄⁺, derived from phosphine.

A hypothetical compound, analogous to ammonium, formed by the union of four atoms of hydrogen and one of phosphorus (PH₄).

The hypothetical radical PH4, analogous to ammonium, and regarded as the nucleus of certain derivatives of phosphine.

the tetravalent positively–charged phosphorus cation R4P+