不ふ落らく

noun, noun which may take the genitive case particle 'no'

impregnable; unassailable

Almost exclusively used in the four-character compound 難攻不落 (なんこうふらく), meaning 'impregnable' or 'unassailable'. Rarely appears independently.

See also: 難攻不落

• その城しろは難なん攻こう不ふ落らくの要よう塞さいとして知しられていた。

  The castle was known as an impregnable fortress.

• 「不ふ落らく」は単たん独どくではあまり使つかわれず、難なん攻こう不ふ落らくの一いち部ぶとして見みかける。

  不落 is rarely used alone; it is mostly seen as part of 難攻不落.