What does Zelda mean?
Commonly a short form of Griselda, from Germanic 'gris' (grey) and 'hild' (battle). A separate Yiddish name Zelda meaning roughly 'blessed/happy' also exists, so the battle sense specifically traces to the Griselda line.
What does Matilda mean?
From the Germanic elements 'maht' (might, strength) and 'hild' (battle), giving the sense 'mighty in battle'. Popularized by the 11th-century Queen Matilda, wife of William the Conqueror.