Disturb and its cousin perturb are words that I assumed had no prefix-less form, but in that case I was wrong. “Turbid” is indeed a word, one that even Microsoft Word recognizes and they don’t accept hitman. It basically means clouded, in both a literal (murky water is turbid) and figurative (a confused person is also turbid).
Turbid showed up in the early seventeenth century from the classical Latin turbidus, muddy or confused. It comes from the verb turbare, to confuse, and is probably from the Greek word for turmoil tyrbe.
Disturbed showed up three centuries before turbid, although initially it just meant to stop or hinder, like an interruption. The other definitions we now have for it, mix up and upset, came along a bit later, which is funny considering they’re actually closer to its classical Latin form, disturbare, which means “throw into disorder”. The dis- prefix means completely, so combined with the above turbare, it’s to confuse completely. Taken in a literal sense, that’s what being thrown into disorder is like : ).
Perturb showed up in the late fourteenth century from the Old French perturber and classical Latin perturbare, which both mean disturb or confuse, especially in terms of the mind. The prefix per- means through, making the word “disturb through”. When you’re perturbed, your mind is disturbed.
Wow, that was a quick one.