Student or Learner
Is write a sentence?
It depends. As one word in spoken English, it could be taken as an imperative, as in, "Write." or even "Write!".
It could be taken as part of a sentence used in spoken language.
What should we do now?
Write. That's what I'm doing. I'm writing.
In the above exchange, "write" is not a sentence. It's part of a sentence. However, in spoken language or conversational language, we often use phrases, parts of sentences, and single words. The sentence that "write" is part of is this, "We should write". It could be part of another sentence, but it's logical, as an example, to say that it's part of the sentence, "We should write".
That is the verb. The implied subject is "You".
Notice that to make the word a sentence, you need to start it with a capital letter and finish it with a period or exclamation mark.