quack
n. countablen. someone who pretends to be a doctor or an expert but does not actually have the skills or training. You use this word to describe a person who sells fake medicine or gives bad medical advice.
n. a person who dishonestly claims to have medical knowledge or other specialised skills. Often used to describe practitioners of fraudulent medicine or those promoting unproven remedies.
Don't listen to that quack; his herbal cures don't work.
The authorities shut down the clinic after discovering the lead surgeon was a quack with no medical degree.
While the internet provides access to vast amounts of health information, it also allows every quack with a social media account to peddle dangerous misinformation to vulnerable patients.
From Middle English quacken, queken (“to croak like a frog; make a noise like a duck, goose, or quail”), from quack, qwacke, quek, queke (“quack”, interjection and noun), also kek, keke, whec-, partly of imitative origin and partly from Middle Dutch quacken (“to croak, quack”), from Old Dutch kwaken (“to croak, quack”), from Proto-West Germanic kwakōn, from Proto-Germanic kwakaną, *kwakōną (“to croak”), of imitative origin. Cognate with Saterland Frisian kwoakje, kwaakje (“to quack”), Middle Low German quaken (“to quack, croak”), German quaken (“to quack, croak”), Danish kvække (“to croak”), Swedish kväka (“to croak, quackle”), Norwegian kvekke (“to croak”), Icelandic kvaka (“to twitter, chirp, quack”).
Clipping of quacksalver (see there for more), of Dutch origin; ultimately related to Etymology 1 above.
Often used as a derogatory term for someone in the medical field.