謹啓[kinkei] Dear Sir or Madam
啓く[hiraku] to enlighten
啓示[keiji] revelation (i.e. divine revelation)
啓発[keihatsu] enlightenment
啓蒙[keimou] enlightenment

啓蟄[keichitsu] "awakening of insects" solar term (approx. Mar. 6, the day on which hibernating insects are said to come out of the ground)
天啓[tenkei] (divine) revelation
拝啓[haikei] Dear (so and so)
啓上[keijou] speaking respectfully
啓迪[keiteki] edification

天魚[amago] land-locked variety of red-spotted masu trout (Oncorhynchus masou ishikawae)
御天気[otenki] weather
コール天[kooruten] corded velveteen
破天連[pateren] Portuguese Jesuits (in Japan in the 16th century)
天鵝絨[tengajuu] velvet

悪天[akuten] bad weather
悪天候[akutenkou] bad weather
悪天使[akutenshi] evil angels
旭日昇天[kyokujitsushouten] full of vigor and vitality (like the rising sun) (vigour)
一天[itten] the whole sky