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

厳粛[genshuku] gravity
綱紀粛正[koukishukusei] eliminating corruption among government officials
自粛[jishuku] self-control
粛として[shukutoshite] quietly
粛学[shukugaku] school purge

粛軍[shukugun] army purge
粛殺[shukusatsu] withering
粛正[shukusei] regulation
粛清[shukusei] (political) purge
粛党[shukutou] cleaning up (political party)