It is a word, an article to be exact. It is also a letter, you can only use it alone as a word.
The larva of a butterfly is called a caterpillar.
A sentence missing a subject or a verb is a fragment.
The word 'in' would be a preposition in the example sentence you gave.
It's the word that describes the noun in the sentence.
The last sentence.
A single word sentence is called a "monosyllabic" sentence in literature.
I called him on the telephone.
connector
A word that can be used to join two parts of a sentence is called a conjunction. Examples include "and," "but," and "or."
A word. Many groups of letters is called a sentence(:
a sentence is called "une phrase" in French
My philosophy is called 'The Golden Rule'.
Your playmate just called.
A pronoun takes the place of a noun called the antecedent.
My supervisor is called Bob!
A translunar visitor is called an alien.
You mean for the sentence you wrote? That's a question.