Yom Kippur is a solemn period of fasting, prayer, and atonement for the Jewish community. It is considered the holiest day in the Jewish year. When greeting someone for Yom Kippur, it is important to keep in mind the somber and reflective tone of the holiday. Here are some appropriate greetings to share:

• "Have an easy fast" or "Tzom Kal" in Hebrew. This greeting acknowledges the difficulty of fasting and expresses the hope that the fast will be manageable.

• "Good Yuntif" or "Yom Tov" in Hebrew, which means "Have a good holy day".

• "Gmar hatimah tovah" or "Gmar tov" in Hebrew, which roughly translates to "a good seal". This greeting references the traditional belief that a persons fate for the coming year is written on Rosh Hashanah and sealed on Yom Kippur.

• "Have a meaningful fast". This greeting emphasizes the spiritual significance of the holiday.

• "Shana Tova" or "Happy New Year". While this greeting is more commonly used for Rosh Hashanah, which comes just a few days before Yom Kippur, it is still appropriate to use during the Yom Kippur season.

It is important to note that saying "Happy Yom Kippur" is not appropriate, as it does not fit the tone of the holiday.