'shyster' is of uncertain origin; it first appears in American English in the late 19th to early 20th century. Several theories exist: it may be a slang formation from English elements, or a borrowing/alteration of German 'Scheißer' (literally 'shitter') used as a general insult, or influenced by Yiddish or other immigrant-language slang.

'shyster' emerged in colloquial American usage as a derogatory term for a disreputable person. Over time, its application often narrowed to refer specifically to unscrupulous lawyers or professional swindlers.

Initially used as a general insult for a disreputable person, the term later came to be especially associated with dishonest lawyers and shady professional practitioners.