The adjectives large and enormous both imply great magnitude. Large is defined as “of more than average size, quantity, or degree,” and enormous is defined as “greatly exceeding the common size or extent.” The main difference between these two descriptors is that large operates within the boundaries of what is average or standard (I don’t want the small skillet; I need the large one!); enormous applies to what is out of the norm or unusual (the young singer has enormous potential). You may have noticed the word norm right there in the middle of the word—that's no coincidence, and it's a good reminder of the mold-breaking nature of the term. Usually when we use enormous, it is to emphasize that something stretches the limits of what seems possible or that it goes beyond what was expected or imagined.
The verb challenge is used a few different ways. It can refer to summoning another person to a contest of skill (I challenge you to a duel!), or to taking exception to something or calling it into question (She challenged the wisdom of the plan). The latter sense is more confrontational than competitive—which brings us to today’s synonym: confront. To confront something is to face and deal with it boldly and directly. One might confront an individual, which suggests communicating verbally with someone and holding them to account, or confront a problem or issue, which suggests taking action to effect change.