why is it not la grande-mere but la grand-mere since it is feminine?

Answer 1

Thank you for using the Jiskha Homework Help Forum. Here are your choices:
grande mère (no hyphen) = a large mother!
grand-maman, grand-mère (with hyphen) = grand mother

Why? Because! Here are some other words to compare:
grand aunt = grand-tante
grand duchess = grande-duchesse (surprise!)
mémé = granny

Answer 2

why not grande-mère??good question

400 years ago, the feminine was grand'mère, grand'tante... the ' simbolized the feminine
in 1932, l'"académie française" changed the ' by -
so it became grand-mère, grand-tante
to the plurial there are two posibilities : grand-mères or grands-mères