pass someone off as

図書館から借りて読んでいる本が途切れたので Merriam-Webster's Vocabulary Builderを読んでいます。
語幹pater/patrの個所の "patrician" の例文を引用します。


They passed themselves off as patricians, and no one looked too closely at where their money came from.

慣用句らしい "passed themselves off as" の意味が分からなかったので辞書を引きます。

"pass (someone or something) off (as something else)" で次の説明がありました。

・Merriam-Webster's Online Dictionary: to cause people to wrongly believe that someone or something is someone or something else: amateurs passing themselves off as professionals

・Farlex Dictionary of Idioms: To pretend someone or something is, or disguise someone or something as, something else.: There are always guys passing cheap watches off as Rolexes in this part of town.