Most of the times it's phrases that get stuck in my head, not usually a singular word. I can recite the 'I was crazy once' endless speech for about as long as I want to because it was stuck in my head for quite a while. Upwards of a week? To the detriment of a friend of mine, the most recent phrase is 'what the sneef? I'm snorfin' here,' which gets grating to anyone who doesn't also have that phrase stuck in their head.
Sometimes it can be words, though. An example would be eccedentesiast, which got stuck in my head based on its meaning, which is simple someone who fakes a smile. Beyond that, it means someone who hides their plans, thoughts, opinions, everything behind a smile. Imagine a person who is always smiling, always agreeable, yet never honest. This could be someone who's playing nice on the surface while having other plans, but imagine someone who's always masking and playing nice, yet never showing their true self... would they even know who they were, at that point? How would you keep track of your own identity if it's never shown? If you've been hiding behind your facade for that long, would you ever want to find out who you are, or would you be too scared to show yourself again, afraid of what you'd find?
Anyway, archaopteryx. A fun word! I like it. The word itself is fun to say, nice to read. And it's a dinosaur, what's not to love? The name matches what it represents and it's a good word.