Daloon,
I can’t remember which dictionary either, but I know what you’re talking about!
So what I learned in linguistics class about the word ‘nuclear’ is that it’s not that it’s impossible to say it. People who say it don’t have a speech impediment or anything. It’s just harder than some other words, for everyone.
It has to do with what phonology and phonetics. If you think about making the /k/ sound and the /l/ sound, they are in different parts of your mouth. To put it simply, the k is in the back, and the l is closer to the front, so it’s hard for people to shift from back to front quickly. For this reason, they will insert a syllable in between. Perhaps it started out as a “mistake” but it’s easier to say, so other people start saying it, and it just becomes accepted. This is a very common way for word pronunciation to change over time (think about Old English and the language of Canterbury tales)
“Whan that Aprill, with his shoures soote / The droghte of March hath perced to the roote / And bathed every veyne in swich licour”
But that does not change the fact that there is an accepted pronunciation, and “nukular” is NOT IT. It’s still annoying, right?