The giant green sea anemone is not really that giant, but here are its adaptations:

1. Having tentacles to sting prey
2. Having patterns to blend into a crowd of other sea anemone
3. Being yellow-green to camouflage in a sea full of algae or plants.

Yes, the word 'giant' is both a noun (giant, giants) and an adjective.

Examples:

Paul Bunyan was a giant who traveled with a blue ox named Babe. (noun)

Dad brought home a giant watermelon, big enough to feed a crowd. (adjective)