A sentence is defined as a group of words that expresses a complete thought. This means that it has a subject and a verb, and it can stand alone as a complete idea.
Examples of one-word sentences:
* Stop! (Imperative sentence)
* Fire! (Exclamatory sentence)
* Help! (Interrogative sentence)
* Yes. (Declarative sentence)
While these sentences are very short, they are grammatically correct and convey a complete thought.
However, it's important to note that while a sentence can consist of just one word, it's usually not very informative or interesting. Most sentences are longer and contain more words to express complex thoughts or ideas.