The quality or state of being lumpy with clods, or the quality of being stupid and dull-witted.
From 'cloddy' plus the noun-forming suffix '-ness'. The word 'clod' originated in Middle English as a term for lumps of earth, and the abstract noun form emerged to describe both physical and mental properties.
The existence of 'cloddiness' as an abstract noun shows how thoroughly medieval English absorbed the metaphor of soil and stupidity—they needed a word for the very concept of being clod-like!
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