Erinaceous means relating to or resembling hedgehogs. If you ever encounter one of these spiky critters while walking in the woods, you could call it a close encounter of the erinaceous kind!
The word erinaceous is used mostly in zoology books or articles, where it can be used to discuss hedgehogs themselves or to hedgehog-like features of other animals. Those attributes could include having short, stiff spines or quills that radiate outward, or the defense mechanism of rolling into a tight ball when feeling threatened. The word is sometimes used figuratively to describe people who are prickly (as in cranky, irritable, or difficult) or very timid (as in having a defensive, shy demeanor).