by Lindy Biller Jen Theodore (n) a compact mass, especially one without a defined or regular shape. Phrases containing lump : 1. Lump of clay , thick and moldable, ready for shaping. The first thing I ever made was a coffee mug for my husband’s 30th birthday. The mug was squat and plain, speckled brown like a bird’s egg. He loved it, posted it on Instagram, drank from it every morning. Its lip was stubbled with imperfections. Its rounded handle was too small for his fingers.