(chemistry) A higher than normal valency (typically involving a transfer of the electrons from the central (hypervalent) atom to the nonbonding molecular orbitals which it forms with (usually more electronegative) ligands)

(chemistry) having a higher than normal valence

(chemistry) any compound which contains more than eight formally assignable electrons in a valence shell directly associated with the central atom in direct bonding with a number of ligands

plural of hypervalent compound