All 5 Uses

allude
in
A Passage to India
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And here came a second invitation, without a rebuke or even an allusion to his slip.†
Chpt 6

allusion = an indirect reference
They attacked one another with obscure allusions and had a silly quarrel.†
Chpt 9 *

allusions = indirect references
Her remarks pleased him, but his mind shut up tight because she had alluded to her marriage.†
Chpt 14

alluded = indirectly referenced
To recount this would have been incredibly painful, it was the one point she wanted to keep obscure; she was willing to give details that would have distressed other girls, but this story of her private failure she dared not allude to, and she dreaded being examined in public in case something came out.†
Chpt 24

allude = to make an indirect reference
He found Aziz overtired and dispirited, and he determined not to allude to their misunderstanding until the end of the evening; it would be more acceptable then.†
Chpt 31

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)