Know why cattywampus was trending last week?
1540s, from Latin allusionem (nominative allusio) "a playing with, a reference to," noun of action from past participle stem of alludere (see allude). An allusion is never an outright or explicit mention of the person or thing the speaker seems to have in mind.
An indirect reference to some piece of knowledge not actually mentioned. Allusions usually come from a body of information that the author presumes the reader will know. For example, an author who writes, “She was another Helen,” is alluding to the proverbial beauty of Helen of Troy.