膝ひざを屈くっする

expression, suru verb (special)

surrender; give in; yield; submit

Idiomatic expression literally meaning 'to bend one's knee', used figuratively for admitting defeat or yielding under pressure. Often implies a formal or dramatic concession.

• 彼かれはついに膝ひざを屈くっして、相あい手ての要よう求きゅうを受うけ