SOMETIMES it is acceptable to use a one-word sentence.
One-word sentences in English come in a few different forms:
questions (example: Who?)
commands (example: Stop!)
clear statements (example: Me.)
location words (example: Here.)
names (example: Jesse.)
A lot of words in English can be one-word sentences. It all depends on the context (the words around it).
A complete sentence, even a one-word sentence, needs to have a noun and a verb. In one-word sentences the subject (noun) or the action (verb) of the sentence is implied. That means it is understood in the context of the sentence or the sentences around it. The subject and/or verb do not need to be stated explicitly (written or spoken).