Where does the word “ergot” come from and What does “ergot” mean?

Sometimes, as many farmers have observed, a seed of rye becomes diseased and is transformed into a fungus growth of dark purple color, in shape strongly resembling a cock’s spur.

The condition was noted by French farmers many centuries ago, and because of the shape they gave this fungus the name argot, cock’s spur.

In modern French this has become ergot and was thus borrowed by us.