I was just thinking today about how common it is for people to misuse homonyms (or even words that sound close, but are not the same). Recently I've seen a few bad ones, so as a public service I will attempt to offer some clarity.
Allude: to make a veiled reference
Elude: to avoid, escape attention
Allusion: that to which one alludes
Illusion: an image or vision which is not real
Ad: short for advertisement
Add: the opposite of subtraction
Which ones annoy you?