Here's why:
* It modifies verbs, adjectives, or other adverbs:
* "He nearly missed the train." (modifies the verb "missed")
* "It was nearly impossible to find a parking spot." (modifies the adjective "impossible")
* "She ran nearly as fast as the wind." (modifies the adverb "fast")
* It indicates degree or extent: It tells us how close something is to happening or being true.
Let me know if you have any other words you'd like to identify!