a feast day的用法和样例：
- The eighth day after a feast day, counting the feast day as one.
- The entire period between a feast day and the eighth day following it.
- "As you summon to a feast day, so you summoned against me terrors on every side.
- In the fourth century Christmas was added to the Church calendar as a feast day.
- When on a feast day Joachim presented himself to offer sacrifice in the temple, he was repulsed by a certain Ruben, under the pretext that men without offspring were unworthy to be admitted.
a feast day的相关资料：