1. A day laborer who loads or unloads cargo from a vessle. Synonyms: dock worker, dock-walloper, docker, dockhand, loader, longshoreman, stevedore, manual laborer, jack. Also used to mean theives who lurk on wharfs. In a newer prejudice, "lumper" is used to mean unaccountable and possibly illegal.
2. A taxonomist who classifies into large groups, based on major characteristics. Antonyms: divider, splitter. A lumper, in this definition, is on one side of a taxonomical debate.