A word is a unit which is a constituent at the phrase level and above. It is sometimes identifiable according to such criteria as
- being the minimal possible unit in a reply
having features such as
- a regular stress pattern, and
- phonological changes conditioned by or blocked at word boundaries
- being the largest unit resistant to insertion of new constituents within its boundaries, or
- being the smallest constituent that can be moved within a sentence without making the sentence ungrammatical.
A word is sometimes placed, in a hierarchy of grammatical constituents, above the morpheme level and below the phrase level.