surd

n (mathematics 数) mathematical quantity, esp a root, that cannot be expressed as an ordinary number or quantity 不尽根: The square root of 5 (5) is a surd. 5 的平方根（5）是不尽根.

supportive, suppose, supposed, supposing, supposition, suppository, suppress, suppressed, suppressible, suppression, suppressor, suppurate, suppuration, supra-, supremacist, supremacy, supreme, supremely, Supt, surcharge, sure, sure-fire, sure-footed, sure-footedly, sure-footedness, surely, sureness, surety, surf, surface, surface mail, surface tension, surface-to-air, surfboard, surfeit, surfer, surge, surgeon, surgery, surgical,