bad back; spineless person
Used both literally for a weak or painful lower back and figuratively for a person who lacks resolve or easily gives in. The figurative use is colloquial and somewhat derogatory.
Lately, my bad back makes it hard to sit for long periods.
He's spineless, so he gives in quickly during negotiations.
Compound of 腰 (lower back) and 弱 (weak). The figurative sense likely derives from the idea that a weak back cannot support a firm stance, metaphorically extending to a lack of resolve.