How do I edit the built-in dictionary (not the user added words)?

[yojitani]

This is very weird. I have found a word that shows up correct in the apple spell checker that is not in the ~/library/Spelling/en file but which is, nevertheless incorrect. The incorrect word is 'dimiensionalizes.' How do I fix this? Just so you know, I found this as a replacement for the word 'dimensionalizes,' which showed up incorrect (and I promptly added it to my dictionary). I was curious about what 'dimiensionalizes' meant, but could not find it in the OED or even on google. Dimensionalizes is a word, dimiensionalizes is not.

It's not like I use this word regularly, but the error irritates me nevertheless.

Thanks!