Learn English – Is the word “stool” an informal word or a formal word

formalityword-usage

Is the word "stool" an informal word or a formal word?
I think it is a kind of formal word, especially a medical word.
It is used in several academic papers and articles, and also doctors like using this word when they want to talk about status of patients' excrements.
However my English teacher(not native speaker) said that the word stool is an informal word, like poo and I should use "feces or excrement" as formal language.
So I told him that I think it looks like a formal word than informal word because basically it is a specialized word.
Then he said that "Native speakers" use the word stool in informal conversation as using phasal verbs like"have a stool", "after stool", or "go to stool".
I have never heard of those kind of expressions before.
Is he correct?

Best Answer

It is only ever used in a formal medical sense, with examples from the sixteenth century.

Stool derives from the name given to an enclosed chamber, or commode, used for producing stools.

The most usual form is in the plural.

d. A discharge of fæcal matter of a specified colour, consistency, etc.; the matter discharged (chiefly pl.). (OED sense 5d).

It is certainly NOT a slang expression, and I have no idea why it would appear in street dictionaries.