Other forms: clods
A clod is a lump of earth, or a slow-witted person. A clod of soil, clods of earth, you great clod.
The insult comes straight from the lump: a clod is dense and inert. Breaking clods is what harrowing does, because seeds need a fine tilth. Clod is also a cheap cut of beef from the neck. Note clodhopper, meaning a clumsy person or a heavy shoe; and that clod and clot are the same word.
1nounclodA lump of earth.
“The farmer broke up the clods of earth with his spade before planting.”
2nounslowA slow-witted person.
“Don't be such a clod; I've explained it to you three times already!”
clod is a lump, or a dull person.
Middle English clod is a by-form of clot, from Old English clot, a lump. Clot and cloud come from the same lump.
Proto-West Germanic
*klott — mass, ball, clump
Old English
clot
Middle English
clod
English, today
clod
From Middle English clod, a late by-form of clot, from Old English clot, from Proto-West Germanic klott (“mass, ball, clump”). Compare clot and cloud; cognate to kloot (“clod”). Alternatively, clod may derive from Old English clod (found in Old English clodhamer (“a kind of thrush”) and Clodhangra), from Proto-West Germanic kloddō (“lump, clod”), from gel- (“to ball up, become lumpy”), related to West Frisian klodde (“clod, lump”), Dutch klodde (“lump, blob”).
Etymology from Wiktionary, CC BY-SA