tetraphosphide

from The Century Dictionary.

• noun A compound of a supposedly more electropositive element or radical with four atoms of phosphorus: as, sulphur tetraphosphide, S.P₄, a substance which, however, has been shown to be merely a solution of sulphur in phosphorus.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry Any phosphide having four phosphorus atoms