In the Chinese philosophical system of Daoism, Tian is often translated as "Heaven" and is mentioned in relationship to its complementary aspect of Di (地), which is most often translated as "Earth". These two aspects of Daoist cosmology are representative of the dualistic nature of Daoism. They are thought to maintain the two poles of the Three Realms of reality, with the middle realm occupied by Humanity (人 Ren).
The semantics of tian developed diachronically. The Hanyu dazidian, an historical dictionary of Chinese characters, lists 17 meanings of tian 天, translated below.
- Human forehead; head, cranium. 人的額部; 腦袋.
- Anciently, to tattoo/brand the forehead as a kind of punishment. 古代一種在額頭上刺字的刑罰.
- The heavens, the sky, the firmament. 天空.
- Celestial bodies; celestial phenomena, meteorological phenomena. 天體; 天象.
- Nature, natural. A general reference to objective inevitability beyond human will. 自然. 泛指不以人意志為轉移的客觀必然性.
- Natural, innate; instinctive, inborn. 自然的; 天性的.
- Natural character/quality of a person or thing; natural instinct, inborn nature, disposition. 人或物的自然形質; 天性.
- A reference to a particular sky/space. 特指某一空間.
- Season; seasons. Like: winter; the three hot 10-day periods [following the summer solstice]. 時令; 季節. 如: 冬天; 三伏天.
- Weather; climate. 天氣; 氣候.
- Day, time of one day and night, or especially the time from sunrise to sunset. Like: today; yesterday; busy all day; go fishing for three days and dry the nets for two [a xiehouyu simile for "unable to finish anything"]. 一晝夜的時間, 或專指日出到日落的時間. 如: 今天; 昨天; 忙了一天; 三天打魚, 兩天曬網.
- God, heaven, celestial spirit, of the natural world. 天神, 上帝, 自然界的主宰者.
- Heaven, heavenly, a superstitious person's reference to the gods, Buddhas, or immortals; or to the worlds where they live. Like: go to heaven ["die"]; heavenly troops and heavenly generals ["invincible army"]; heavenly goddesses scatter blossoms [a Vimalakirti Sutra reference to "Buddha's arrival"]. 迷信的人指神佛仙人或他們生活的那個世界. 如: 歸天; 天兵天將; 天女散花.
- Anciently, the king, monarch, sovereign; also referring to elders in human relationships. 古代指君王; 也指人倫中的尊者.
- Object upon which one depends or relies. 所依存或依靠的對象.
- Dialect. A measure of land [shang, about 15 acres]. 方言. 垧.
- A family name, surname. 姓.
- A material or physical T'ien or sky, that is, the T'ien often spoken of in apposition to earth, as in the common phrase which refers to the physical universe as 'Heaven and Earth' (T'ien Ti 天地).
- A ruling or presiding T'ien, that is, one such as is meant in the phrase, 'Imperial Heaven Supreme Emperor' (Huang T'ien Shang Ti), in which anthropomorphic T'ien and Ti are signified.
- A fatalistic T'ien, equivalent to the concept of Fate (ming 命), a term applied to all those events in human life over which man himself has no control. This is the T'ien Mencius refers to when he says: "As to the accomplishment of a great deed, that is with T'ien" ([Mencius], Ib, 14).
- A naturalistic T'ien, that is, one equivalent to the English word Nature. This is the sort of T'ien described in the 'Discussion on T'ien' in the [Hsün Tzǔ] (ch. 17).
- An ethical T'ien, that is, one having a moral principle and which is the highest primordial principle of the universe. This is the sort of T'ien which the [Chung Yung] (Doctrine of the Mean) refers to in its opening sentence when it says: "What T'ien confers (on man) is called his nature." (1952:31)
For the etymology of tian, Schuessler (2007:495) says, "Because the deity Tiān came into prominence with the Zhou dynasty (a western state), a Central Asian origin has been suggested." He cites the Mongolian word tengri "sky, heaven, heavenly deity" or the Tibeto-Burman words Adi taleŋ and Lepcha tǎ-lyaŋ "sky". Schuessler (2007:211) also suggests a likely connection between Chinese tiān 天, diān 巔 "summit, mountaintop", and diān 顛 "summit, top of the head, forehead", which have cognates such as Naga tiŋ "sky".