Etymologically it is a nominalized adjective formed with a -ios suffix from the stem Dionys- of the name of the Greek god, Dionysus,[1] parallel to Apollon-ios from Apollon, with meanings of Dionysos' and Apollo's, etc.
The exact beliefs attendant on the original assignment of such names remain unknown.
The feminine version of the name is Dionysia, nominative case, in both Greek and Latin.
The name of the plant and the festival, Dionysia, is the neuter plural nominative, which looks the same in English from both languages.
The latter names have lost the suffix altogether, using Old French methods of marking the feminine, Denise.