tiān

Heaven, the sky, a day, the weather, celestial ; the Emperor, great, high, any superior over an inferior; moral superiority

大 dà great, is the radical, but the meaning of the character is not the one 一 great 大 as it is often translated, but the one sky 一 which is over man 大 ; thus it is an indicative character, not a logical combination.

Compounds

春天 chūntiān – spring
夏天 xiàtiān – summer
秋天 qiūtiān – autumn/fall
冬天 dōngtiān – winter
前天 qiăntiān – the day before yesterday
昨天 zuótiān – yesterday
今天 jīntiān – today
明天 míngtiān – tomorrow
后天 hòutiān – the day after tomorrow
星期天 xīngqītiān – Sunday
天气 tiānqì – the weather
天天 tiāntiān – every day
天蓝 tiānlán – blue, azure
天下 tiānxià – the world (under the sky)

Learn more about 天 at Wikionary