E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To make a mull of a job is to fail to do it properly. The failure of a peg-top to spin is called a mull, hence also any blunder or failure. (Scotch, mull, dust, or a contraction of muddle.) The people of Madras are called Mulls, because they are in a less advanced state of civilisation than the other two presidencies, in consequence of which they are held by them in low estimation. (Anglo-Saxon, myl, dust.)