1A nickname or form of address for: a person or animal who slobbers; one who drools copiously or excessively; a messy or noisy eater or drinker; a wet or enthusiastic kisser.
Now more frequently of animals than people.
2 rare As a general term of abuse or contempt: a stupid, contemptible, or ineffectual person.
Late 17th century; earliest use found in John Dryden (1631–1700), poet, playwright, and critic. Either (i) from slobber + the plural of chop.