“体弱的”的英语可以翻译为：infirm ...

实力较弱的网络公司倒闭了。The weaker dot-coms have collapsed.袭击舰即便最后被它们团团围住, 它也会摧毁其中一艘较弱的巡洋舰, 突围而出.The raider, cornered at length, will overwhelm one weak vessel and escape.他一直帮助力量较弱的一方.He has always supported the weaker party....

“瘦弱的”的英语可以翻译为：emaciated，scraggy，thin and weak，weedy ...

“贫弱的”的英语可以翻译为：cutcha，jejune ...