Merriam-Webster's Word of the Day for May 22, 2013 is:

canker • \KANK-er\  • verb
1 : to become infested with erosive or spreading sores 2 : to corrupt the spirit of 3 : to become corrupted

Examples:
"I have never seen any children, only debased imitations of men and women, cankeredA Lady's Life in the Rocky Mountains, 2005

"If you have dead or cankered branches on your trees, disinfect pruning tools between cuts to prevent chances of spreading fire blight bacteria from infected trees." — From an article in the Argus Leader (Sioux Falls, South Dakota), March 13, 2013

Did you know?
"Canker" is commonly known as the name for a type of spreading sore that eats into the tissue—a use that obviously furnished the verb with both its medical and figurative senses. The word ultimately traces back to Latin "cancer," which can refer to a crab or a malignant tumor. The Greeks have a similar word, "karkinos," and according to the Ancient Greek physician Galen the tumor got its name from the way the swollen veins surrounding the affected part resembled a crab's limbs. "Cancer" was adopted into Old English, becoming "canker" in Middle English and eventually shifting in meaning to become a general term for ulcerations. "Cancer" itself was reintroduced to English later, first as a zodiacal word and then as a medical term.