 Nouns in "-eas" stem from the ancient third declension and form their plural respectively.Moreover, there are other categories and forms too that have to do with either Demotic or Katharevousa.For example, through Demotic, many nouns, especially oxytones (those that are accented on the last syllable) in -άς ("-as") or -ής ("-is") form their plural by adding the stem extension -άδ- ("-ad-") and -ήδ- ("-id-") respectively.