deposit 我觉得这个常用点.(楼上说的其他单词也正确.)
eg.
1.买房者下星期付定金.
The purchaser of the house will pay the deposit next week.
2.在预订时交付定金是一般的[普遍遵守的]惯例.
It is accepted/standard practice to pay a deposit with one's order.