A sentence must have more than one word?

That's a great question! It depends on how you define a "sentence".

Traditional Grammar:

* Yes, a sentence in traditional grammar needs at least two words: a subject and a verb. For example: "He runs."

Linguistics:

* Linguists sometimes define sentences more broadly, considering single-word utterances as complete sentences. For example, "Fire!" or "Stop!" can be considered complete sentences in certain contexts, conveying a clear message.

So, the answer is:

* Technically, yes, a sentence typically needs more than one word according to traditional grammar.

* But in linguistics, single-word sentences can exist in specific situations.