Before revision: In modern English, tumorthe is used as a synonym for a neoplasm (a solid or fluid-filled cystic lesion that may or may not be formed by an abnormal growth of neoplastic cells) that appears enlarged in size.
After revision: In modern English, tumor (non-US spelling: tumour) is used as a synonym for a neoplasm (a solid or fluid-filled cystic lesion that may or may not be formed by an abnormal growth of neoplastic cells) that appears enlarged in size.