Is it true that is ain't a word in the webster dictionary based on the following text?

Webster's Third New International Dictionary, published in 1961, went against then-standard practice when it included the following usage note in its entry on ain't: ''though disapproved by many and more common in less educated speech, used orally in most parts of the U.S. by many cultivated speakers esp. in the phrase ain't I.'' Many commentators disapproved of the dictionary's relatively permissive attitude toward the word, which was inspired, in part, by the belief of its editor, Philip Gove, that ''distinctions of usage were elitist and artificial.''
yes