Imposter is an alternative spelling of the same noun. Impostor is the proper spelling of this word, but imposter has also appeared frequently for several centuries.

Is there a word imposter?

"Some imposter who wished to come into the town barefoot, perhaps, and so excite our sympathies," said Miss Chant. He wanted to run, to burst away from the imposter, but the guy was shaking so hard Bart couldn't just leave him standing there. "Some imposter must have assumed it," suggested the officer.

What do you mean by imposter?

: a person who deceives others by pretending to be someone else. impostor.