The smiling boy was nicknamed sharptooth by his friends because of his two prominent front teeth.

sharptooth 是一个复合词，由 sharp（锋利的）和 tooth（牙齿）组成。sharp 在这里形容牙齿的形状像刀锋一样尖锐突出，tooth 指牙齿。sharptooth 字面意思是"锋利的牙齿"，用来形容门牙特别突出的样子。