septentrional northern
Actually, this word is used in English as well, but when I've come across it, it has been in Spanish. I tend to remember that it's a direction but forget which one. Instead I just associate it with the number seven, which is no help at all.
But I finally looked up the etymology and it is related to the number seven and maybe that is some help after all... from Latin septem (“seven”) + triō (“plow ox”) which refers to the constellations Ursa Major and Ursa Minor which are in the north. So basically it's an adjective meaning "[the direction] of the seven oxen [in the sky]".
We'll see if that's enough to help me remember or if it's too convoluted to stick (maybe I'll only remember "oh yeah, it did have something to do with the number seven after all...." which will still be no help, if that's all I remember. LOL)