pent- en · X Meanings (alt-of, alternative, morpheme) Alternative form of penta- used before a vowel. alt of penta- used before a vowel (morpheme) Used for the digit five 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”) + pent- (“5”) + -ium (element suffix) → unbipentium (“element 125”) Relateds -pent-