What part of speech is the word thoughest?

"Thoughest" is not a standard word in the English language. It seems like a possible misspelling of "toughest."

If you meant toughest, then it is an adjective.

Here's a breakdown:

* Tough is the base adjective.

* -est is the superlative suffix, indicating the highest degree of toughness.

So, toughest describes something that is the most tough or difficult.