What does Rosalind mean?
Disputed etymology. Originally Germanic, from 'hros' (horse) + 'lind' (soft, tender), i.e. roughly 'gentle horse'. In Romance-speaking areas it was reinterpreted by folk etymology as Latin/Spanish 'rosa linda' meaning 'beautiful rose'. The floral meaning is the popular later reading, not the original.
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.