Are they escaping or are you referring to them? That’s an odd sentence, but it’s what you need to consider when you’re choosing between these two words. They are used in different ways, too, which helps!

To elude means to escape from or evade, usually in some kind of skilful or cunning way (this can be concrete or abstract – “The moth eluded me and flew out of the window”; “The meaning of his ideas eluded me”). Note that elude has one l and something eludes something else.

To allude to something means to hint at it indirectly, or mention it in passing: “When discussing Betty he alluded to her plastic surgery but it was not the main part of the conversation”. “‘Ah, the majesty of your figure,’ said Adrian. ‘Are you alluding to my boob job?’ shrieked Betty”. Note that it has a double l and someone alludes to something else. Also note that this is sometimes used mistakenly in place of refer. You can’t say “He alluded to the actress by her name”, as to allude is to be indirect. Here you would use “He referred to the actress by her name”. Save allude for a use such as, “He alluded to the actress, mentioning an infamous role she played earlier in her career but not naming her”.

And to illude (has anyone ever used this?) means to trick or delude. But it’s hard to see when either of those words wouldn’t do, and it saves you remembering this one. I am just including it for the sake of completeness, to be honest. It is important when it comes to the word formed from it, illusive, though …

A bonus section today …

If something (language, on the whole) is allusive, it means it uses suggestion (yes, alluding to something) rather than mentioning something explicitly. “The poet uses allusive language to describe the pile of droppings without mentioning what it actually is”.

If something is elusive, it is difficult to achieve, find, catch, etc. It aims to elude the person who is trying to catch it. “The moth proved elusive, as I chased it around the bathroom, and it escaped through the window”.

If something is illusive, it is illusory and deceptive – it’s main purpose is to illude. “His wealth was illusive – all fur coats on top, all cheapo clothes underneath” (wealth can be elusive, of course, too, if you can never manage to achieve it, but the meaning is different).

You can find more troublesome pairs here and the index to them all so far is here.