word

• one of the units of speech or writing that native speakers of a language usually regard as the smallest isolable meaningful element of the language, although linguists would analyse these further into morphemes (Collins dictionary)
• any of the sequences of one or more sounds or morphemes (intuitively recognized by native speakers as) constituting the basic units of meaningful speech used in forming a sentence or sentences in a language (Oxford English dictionary)
• usually the easiest units to identify, in the written language
  in most writing systems, they are the entities that have spaces on either side ("A Dictionary of Linguistics and Phonetics, D. Crystal)

Should there be any more definitions after the above?
If the native speakers regard a word to be "the smallest isolable meaningful element of the language," but, by definition, it isn't, why does this concept persist?

Be that as it may, here, the remaining definitions:

• an instance of vocal intercourse; chat, talk, or discussion
• an utterance or expression, esp a brief one
• news or information
• a verbal signal for action; command
• an undertaking or promise
• an autocratic decree or utterance; order
• a watchword or slogan, as of a political party
• computing
  a set of bits used to store, transmit, or operate upon an item of information in a computer, such as a program instruction