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极瘦弱的人；无家可归者;流浪儿
If you refer to a child or young woman as a waif, you mean that they are very thin and look as if they have nowhere to live.
例句
...a dirty-faced waif of some five or six years...
五六岁大、脸上脏兮兮的流浪儿
The director wants a waif-like, teenage girl with long, dark hair for the role.
导演想要一个留着乌黑的长发、面黄肌瘦的十来岁女孩扮演这个角色。