An agent noun is one which lurks behind adverbs and then springs out and shoots down enemy participles...
...oh all right: it isn't really. That would make grammar cool, and everyone knows it's not - well, not in that way, anyway.
(Though on the plus side, grammar does drive people to the heights of fury and viciousness, so you can't say it's dull.)
Anyway, an agent noun is a word where (in English) the ending -or or -er (usually) has been tacked on to turn an action into the person doing that action.
Teacher is an action noun. So is baker and dancer and blender. But not grocer or butcher.
Today I'm a learner.
Words To Use Today: an agent noun. (By the way, the word grocer comes from the Old French grossier, from gros, which means large; and the word butcher comes from the Old French bouchier and is probably related to the Welsh word bwch, which means billy goat.)