( informal ) hardly able to stand because of emotion, fear, illness, etc. :
His sudden smile made her go weak at the knees.
( informal ) hardly able to stand because of emotion, fear, illness, etc. :
His sudden smile made her go weak at the knees.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005