Final answer:
In the sentence, the word margin is used as a noun to refer to the edge or outer limit of the forest.
Step-by-step explanation:
In the sentence "Shelbie wanted to hike to the margin of the forest," the word margin is used as a noun. According to the dictionary entry provided, margin is defined as a "spare amount or degree allowed" or "part of a page or sheet of paper." In this sentence, it is referring to the edge or outer limit of the forest.
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