Used with he, she, it, or a singular noun to form the negative in the present simple tense.
Sarah doesn't eat meat because she is a vegetarian.
This old car doesn't start on cold mornings.
✦ A contraction of "does not", combining the third-person singular present tense form of the verb "do" (from Old English "dōn", meaning to perform or put) with the negation "not" (from Old English "nāwiht", meaning no thing), common in English since the 16th century.
the short form of do not, used to make a verb negative
I don't want any more cake.
They don't live in this city anymore.
✦ shortened from the words do and not in the 17th century
