infirm
/ɪnˈfɜ:m; ɪn`fəm/ adj
1 physically weak (esp from old age or illness) 体弱的, 虚弱的, 衰弱的（尤指因年迈或疾病）
walk with infirm steps 迈著虚弱的步子行走.
2 ~ of sth (fml 文) without strength of sth 欠缺某方面的力量
infirm of purpose, will, etc, ie not purposeful, not resolute 目的不明确、 意志不坚强.