die out

verb

1. To become extinct.

   “The dinosaurs died out a long time ago.”

   “The original family who had begun to build a palace to rival Nonesuch had died out before they had put up little more than the gateway,[…].”

2. To cease gradually.

   “The prejudice has died out.”

   “However, apart from all this, the Chief was a grand old man, belonging to a class of individualists which seems to be dying out in these days, when standard behaviour seems to be as prevalent as standard designs.”