Mixed-up, man­gled expres­sions; foreign-language faux pas; con­fused and con­fus­ing terms; com­monly mis­pro­nounced words — they’re all explained in Com­mon Errors in Eng­lish by Paul Brians.

The con­cept of lan­guage errors is a fuzzy one. I’ll leave to lin­guists the tech­ni­cal def­i­n­i­tions. Here we’re con­cerned only with devi­a­tions from the stan­dard use of Eng­lish as judged by sophis­ti­cated users such as pro­fes­sional writ­ers, edi­tors, teach­ers, and lit­er­ate exec­u­tives and per­son­nel offi­cers. The aim of this site is to help you avoid low grades, lost employ­ment oppor­tu­ni­ties, lost busi­ness, and tit­ters of amuse­ment at the way you write or speak.

It’s avail­able on Ama­zon, but when it’s avail­able free online and is updated reg­u­larly, why buy? The sup­ple­men­tary pages are also worth a look (non-errors, more errors, and com­monly mis­spelled words).