Means 'life' -- a popular greeting is 'L'chayim' meaning 'to life.' In Jewish mysticism, the numeric value of words are often added up to find hidden meanings in words. The letters comprising "Chai' equal a total of 18, hence the practice of giving money and donations in increments of 18 dollars.
(KHAHY, rhymes with Hi!) Lit. living or life. The word is often used as a design on jewelry and other ornaments. Donations to charity are often made in multiples of 18, the numerical value of the word.