In the Hebrew language, the word chai (חַי) spelled by these two letters means "living," is related to the term for "life," chaim, and also appears in the slogan "'am yisrael chai!"
(עַם יִשְׂרָאֵל חַי , "The nation of Israel lives!", referring to all Jews ).

There have been various mystical numerological speculations about the fact that, according to the system of gematria, the letters of chai add up to 18. For this reason, 18 is a lucky number in Judaism, and many Jews give gifts of money in multiples of 18 as a result.