“وَ” (wa)a joining word meaning “and.” It connects this word to what came before.Corpus grammarCONJ — prefixed conjunction wa (and).
“كَأْسًا” (kaʾasanā)means “And a cup” in this verse. It is a noun. a naming word. Here it is masculine, not specific, accusative.Corpus grammarN — accusative indefinite noun.