back out译为退出收回食言，违约，是动词短语，例如：

1.He put his back out lifting the crates.他搬大木箱时脊椎脱了臼。

2.I gave her a lift back out to her house我让她搭我的便车回家。

3.She could not， in good conscience， back out on her deal with him.凭良心她不能背弃与他达成的协议。