Nova
late 19th century: from Latin, feminine of novus ‘new’ (because such stars were thought to be newly formed).
wiktionary
Feminine nominative singular of Latin novus(“new”). The feminine is used since stella(“star”) is feminine; thus nova is a shortening of nova stella(“new star”), first used in this sense in 1573 by Tycho Brahe.
etymonline
nova (n.)
"star that suddenly increases in brightness then slowly fades," 1877, from Latin nova, fem. singular adjective of novus "new" (see new), used with stella "star" (a feminine noun in Latin) to describe a new star not previously known (Tycho Brahe's published observation of the nova in Cassiopeia in 1572 was titled De nova stella). Not distinguished from supernovae until 1930s (Tycho's star was a supernova). The classical plural is novae.
