A tumor or tumour's the name for a swelling or lesion formed by an abnormal growth of cells (termed neoplastic). Tumor isn't synonymous with cancer. A tumor can be benign, pre-malignant or malignant, whereas cancer's by definition malignant. Etymology The term tumor's derived, via the Old French tumour, from the Latin tumor "swelling". It originally meant an abnormal swelling of the flesh. In contemporary English, tumor's synonymous with solid neoplasm, all other forms of swelling being called… (More on Tumor)