Definition of "but if" [but if]

• Unless. (conjunction)

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• "Clearly, making use of prediagnostic biomarker technology to determine who will eventually be struck with an autoimmune disease will only be useful if that technology is not only foolproof, but if we possess fail-safe and side-effect-free interventions to offer to those who are informed by their doctors that they sit at the precarious edge of disease."
• "Not just because I was editor of the News of the World at the time, but if the accusations are true, the devastating effect on Milly Dowler's family is unforgivable."
• "He had never heard of any quicksand in Blight County but if there was any, count on an FBI agent to find it."