Sentence:  Among common errors still persisting in the minds of educated people, one error which dies very hard is the theory that a <WSD>dialect</WSD> is an arbitrary distortion of the mother tongue, a wilful mispronunciation of the sounds, and disregard of the syntax of a standard language. 
Meaning of the word marked with <WSD> tags:  A lect (often a (regional) or (minority) language) as part of a group or family of languages, especially if they are viewed as a single language, or if contrasted with a standardized idiom that is considered the 'true' form of the language (for example, Cantonese as contrasted with Mandarin Chinese, or Bavarian as contrasted with Standard German).