The term BITER DOG can be solved by the crossword solution FLEA, which is a four letter word. Fleas are small, wingless parasites that feed on the blood of mammals and birds. They are known to cause skin irritation and transmit diseases. Fleas are often associated with dogs, as they can live in their fur and bite them. Therefore, the term BITER DOG could refer to a dog that has fleas, or a dog that bites due to irritation caused by fleas.