Meaning

noun any malignant growth or tumor caused by abnormal and uncontrolled cell division; it may spread to other parts of the body through the lymphatic system or the blood stream

noun (astrology) a person who is born while the sun is in Cancer

noun a small zodiacal constellation in the northern hemisphere; between Leo and Gemini

originBorrowed from Latin cancer (“crab”), a calque of Ancient Greek καρκίνος (karkínos, “crab; ulcer; cancer”) (possibly cognate), applied to cancerous tumors because the enlarged veins resembled the legs of a crab. Doublet of canker and chancre.

Etymology from Wiktionary, CC BY-SA 3.0