早 (zǎo) means early as an adjective and adverb, and as a standalone greeting it functions as an informal good morning (similar to morning! in English). The antonym is 晚 (wǎn, late). Common compounds: 早上 (zǎo shàng, morning), 早饭 (zǎo fàn, breakfast), 早安 (zǎo ān, good morning - formal), 早起 (zǎo qǐ, to get up early). The Chinese proverb 早起的鸟儿有虫吃 is the equivalent of the early bird catches the worm.