An allusion is an indirect reference to something.|
An illusion is deception.
AllusionThe noun allusion denotes a subtle or indirect reference to something (i.e., a hint at something). It derives from the verb to allude.
The Simpsons is full of allusions to well-known films.
His consistent allusions to being so poor as a child are not in keeping with his brother's version of their childhood.
IllusionAn illusion is a false impression or deception.
It's not an oasis — it is an illusion.
I am under no illusion how much work is required.