prefix
Prefix attached to nouns to mean something is fake, pretend, or not genuine. Often carries a negative or dismissive tone.
彼はエセ専門家の意見に惑わされた。
He was misled by the opinion of a pseudo-expert.
あの店はエセブランド品ばかり売っている。
That shop sells nothing but fake brand-name goods.
Very rare kanji form; it is rarely used.
にせ is a noun meaning 'fake' or 'imitation' and can be used as a prefix, but エセ is more colloquial and often implies a pretentious or deceptive quality rather than just being counterfeit.
なんちゃって is a very casual, jocular prefix meaning 'just kidding' or 'pretend', often used self-deprecatingly, while エセ is more critical and can be used in serious contexts.
The origin is uncertain. It may be related to the classical Japanese adjective えせし (eseshi) meaning 'poor' or 'inferior', but the exact derivation is unclear.