The Allen and Greenough is still under construction;
so some links may not work quite the way you would expect.
Names of Actions and Abstract Nouns.
237. Names of Actions are confused, through their
terminations, with real abstract nouns (names of qualities), and
with concrete nouns denoting means and instrument.
They are also used to express the concrete result of an action
(as often in English).
Thus legió is literally
the act of collecting, but comes to mean legion (the body of soldiers collected); cf. levy in English.