1. An emphatic negation indicating the absence of any single item or person from a group; a stronger way of saying 'not one'
Not even one person showed up to the meeting.
Nem uma sequer pessoa apareceu na reunião.
2. Used to emphasize that something did not happen at all, not in the slightest
He didn't thank me, not even one time.
Ele não me agradeceu, nem uma única vez.