noun
sham; fraud; counterfeit; impostor; pretender
Refers to a person or thing that is not genuine; a fake, phony, or impostor. Often used in a derogatory sense.
彼は医者を名乗っているが、実は似非者だ。
He claims to be a doctor, but he's actually a fraud.
その骨董品は似非者だとすぐに分かった。
I immediately knew that antique was a counterfeit.
詐欺師 specifically means 'swindler' or 'con artist', focusing on the act of defrauding others for financial gain. 似非者 is broader, covering any kind of sham or pretender.
似非 (ese) means 'pseudo-' or 'sham', and 者 (mono) means 'person'. The exact origin of 似非 is uncertain, but it has been used since classical Japanese to indicate something false or pretended.