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

急度[kitto] surely
オリエント急行[orientokyuukou] Orient express
応急[oukyuu] emergency
応急攻撃[oukyuukougeki] hasty attack
応急渡河[oukyuutoka] hasty crossing

火急[kakyuu] emergency
緩急[kankyuu] pace
危急[kikyuu] emergency
危急存亡[kikyuusonbou] life-and-death matter