* Constantly evolving language: New words are created, and old ones fall into disuse all the time. What is rare today could be common tomorrow.
* Usage varies: Word frequency depends on context. A word might be common in scientific writing but rare in everyday conversation.
* Data limitations: We don't have a complete record of every single word ever used in English.
However, we can point to some strong contenders for least used words:
* Extremely obscure words: Words found only in specific fields like technical jargon or archaic literature.
* Proper nouns: Names of people, places, or things that are unique and less likely to be used frequently.
* Very specialized vocabulary: Words related to specific hobbies, professions, or cultures.
Instead of focusing on finding the "least used" word, it's more interesting to explore the fascinating world of rare words and their origins.
Some resources like the Oxford English Dictionary and Google Ngram Viewer can help you find interesting and less common words in the English language.