Compounds of 曰

• 曰う
  (v4h) (uk) (pol) to say
  to be pleased to say (hint of sarcasm)
• 曰く
  (n,n-adv,v5k) (1) to say
  to reason
  (2) pretext
  history
  past
  story
• 曰く付き
  (n,adj-no) with an interesting history (story)
  with a shady history
  with circumstances that are difficult to explain
• 曰く言い難し
  (exp) It is hard to explain
  It is hard to say