What is a word?

The process of evolution and coinage of new words never ceases to fascinate me, yet I find myself cringing at the use of words which were created by the bastardizing of nouns into verbs, for example “liaise” and “incentivize,” neither of which will I accept in written works I review for publication (although I admit that “liaise” is in Merriam-Webster’s dictionary, it is labeled a British colloquialism and therefore I reject it in formal American writing). I have only recently become resigned to the word “syncing.” Which begs the question: At what point does a word become acceptable in formal usage? How about if a word has been in use for hundreds of years? According to Merriam-Webster, the precursor to the word “ain’t” was first used in 1618 – but ain’t is still considered to be a “nonstandard” contraction. Obviously a word associated with a new invention, such as the Internet or the smartphone, receives the imprimatur of society almost immediately, since it has hardly any competition. So … what makes a word legitimate?