The part of speech that modifies a verb, adjective, or other adverb.
What does it mean to describe a man as an adverb, as Stephen Crane describes the gambler in the closing paragraphs of The Blue Hotel? It seems to invalidate his existence, or at least his participation in the story. The semantics are easy enough to grasp. While the gambler was the man who actually killed the Swede on that fateful night, it seems that the author believes that he was acting only as an extension of the will of the other participants in the story.
This viewpoint is enhanced by the way that the characters are developed and presented in the story. The character of the gambler is barely introduced--it's even pointed out that he conducts himself in a nondescript kind of manner--so as not to call attention to himself. The other characters, on the other hand, are thoroughly introduced, and a great deal of time is spent with them, allowing us to get a clearer picture of who they are.
Is the author justified in this viewpoint? I think so. Johnny's cheating led to a fight, and the others' refusal to believe the Swede sent him on his way to his death. In this regard, the Easterner (believed by many to be the literary alter ego of Crane) is even more culpable that the rest--he knew Johnny cheated and failed to stand up for the Swede, guaranteeing his doom. Turns out the Swede was right--he never did get out of Romper alive.