Sister – hermana
Pronounced ehr-mah-nah (remember the "h" is silent in Spanish)
To remember that sister is pronounced ehr-mah-nah (hermana) in Spanish, use the following mnemonic:
She looked very different to her sister and her manner (hermana) was totally different too.
It's so obvious that hermana is feminine (la hermana) that we decided not to include a "lady" image for this one.