1. A solid piece of something; such as, a solid clump of soil: The gardener was busy breaking up the large lumps of dirt before planting his new vegetable garden.
2. An abnormal protuberance or localized enlargement on the body: Jane asked, "William, how did you get that lump on your head?"

To put things or people into the same group or area, even if they don't belong together: When you listen to talk-show hosts, the rightists lump all of the leftists together and the leftists lump all of the conservatives together.