the name Zygarde comes from,
A letter representing third coordinate axis ( and proof that the next game is Pokemon Z) Note: Pokemon Sun and Moon...
and the french word for guard,
the -e is silent in the word garde, which is pronounced gärd.
this is the same as the english word guard, and the pronunciation of Gardevior ( gärd-ä-vwär)
another Pokemon, and therefore Zygarde is called zī-gärd