Do you associate some words with completely unrelated words/ideas?

That seems like a form of sex daily dyslexia, where the letters get jumbled up in your head. Although Nepotism and Poseidon don't have all exactly the same letters, they are kinda close to being anagrams of each other.

I guess it's not exactly the same, because it sort of is related, but I always get tripped up on "ancillary" because it is a totally inoffensive English word... except that the Latin word ancilla means "slave girl."

The Roman equivalent to the Greek Poseidon was Neptune.

nepotism, I think of the Greek god Poseidon.

But that is easily explained:

Once upon a time you have played with anagrams. These are not exactly anagrams, but you wished they were. And so you decided to remember it.

Every time I hear nepotism, I see a mini Napoleon Bonaparte in my head... Weird, I know

A few word pairs that are tightly related in my brain, but unrelated to everybody else.

I won't tell them.

I use them for the "secret question / secret answer" thing with passwords. I will not forget them.

When the question is only one word, and the answer is unrelated, then no hacker can ever guess the correct answer.