慇いん懃ぎんを通つうじる

expression, ichidan verb

have a secret sexual relationship; have an illicit love affair

A euphemistic set phrase for a clandestine sexual relationship, often implying adultery or a socially disapproved affair. The expression uses 慇懃 (courtesy, politeness) ironically to suggest outward propriety masking an intimate liaison.

• 二人ふたりは長なが年ねん慇いん懃ぎんを通つうじていたが、ついに周しゅう囲いに知しられてしまった。

  The two had been carrying on a secret affair for years, but finally people around them found out.