hex- en · X Meanings (alt-of, alternative, morpheme) Alternative form of hexa-, usually used before a vowel. alt of hexa-alt of usually used before a vowel (morpheme) Used for the digit six to form systematic element names of elements whose existence has been predicted, and which have not yet been given a trivial name. un- (“1”) + bi- (“2”) + hex- (“6”) + -ium (element suffix) → unbihexium (“element 126”)