* It depends on what you consider a "word": Do you include proper nouns like "a" or "I"? Do you allow contractions like "a" or "I'm"?
* Different dictionaries have different rules: Some dictionaries include words that are only used in specific contexts, while others focus on commonly used words.
Some contenders for the shortest word include:
* "a" (definite article)
* "I" (pronoun)
* "O" (interjection)
* "A" (article)
Ultimately, there isn't a definitive answer to the question of the shortest word in the dictionary.