[arbitrage]

It's a perfectly cromulent word.

In american irregular usage, it's a known word, but the primary reason someone would use it (other than incidentally or acidentally) is to effect an affect; that is to say, the author might have used this word on purpose to draw your attention.

This type of usage is much more common in, for example, poetical writings; it is also used semifrequently in opinion or persuasive writings. The author Stephen King employs this mechanism very frequently. He loves using weird americanisms to evoke a feeling of alienation from his audiences.