Folk etymology is when an unfamiliar word is altered through common use to resemble a more familiar word. Hence, through the process of folk etymology cater corner becomes kitty corner . Functional Shift Words often shift their grammatical function over time. Nouns become verbs, verbs become nouns, nouns become adjectives, etc. Run was originally a verb, dating back to about the year 800, but in the 15th century people started using it as a noun, as in to go for a run .
Some grammarians decry functional shifts as improper English, but it is a natural process.
There are four distinct sub-classes of word formation through abbreviation . These are initialisms, acronyms, clipped forms, and back formations. In initialisms and acronyms , the initial portions of the words or syllables of a phrase are used to from a word. Note that acronymic word origins are a twentieth century phenomenon. This method of word formation is unknown in earlier periods.