I would like to know if there is a keyword that basically means 'if the creature has a power of at least X'. A friend told me there might be, but I couldn't find it. I wouldn't be surprised if I missed it, so I'd like to know if anyone here has heard of it.
There is no such keyword ability, and no other word used in that specific context. Whenever a card has an effect that depends on the power of the creature, it's usually phrased as an English sentence, i.e. "Creatures with power less than Aura Gnarlid's power can't block it." on Aura Gnarlid