All 4 Uses

allude
in
The Man Without a Country
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everybody was permitted to lend him books, if they were not published in America and made no allusion to it.
Chpt Rest *

allusion = reference
He had almost all the foreign papers that came into the ship, sooner or later; only somebody must go over them first, and cut out any advertisement or stray paragraph that alluded to America.†
Chpt Rest

alluded = indirectly referenced
I remember it, because poor Phillips, who was of the party, as soon as the allusion to reading was made, told a story of something which happened at the Cape of Good Hope on Nolan's first voyage; and it is the only thing I ever knew of that voyage.†
Chpt Rest

allusion = an indirect reference
He never alluded so directly to his story again; but from one and another officer I have learned, in thirty years, what I am telling.†
Chpt Rest

alluded = indirectly referenced

Definitions:

(1) (allude)
to make an indirect reference

The expression, no allusion can mean "not even an indirect reference"; i.e., neither a direct nor an indirect reference to something.
(2) (meaning too rare to warrant focus)