measure word, noun, time word, numeral, punctuation, pronoun, verb, adjective · a unit of time equal to twenty-four hours

他在北京住了三天。

noun, place name, modal particle, adverb · the atmosphere and outer space as seen from the earth

深秋的天总是那么高，那么蓝，看不见一丝云朵。

noun, idiom, verb · the abode of God or the gods; divine providence or nature

这是上天的安排。