Is Mr. a contraction of 'mister' or 'master'?

Typically Mr. is a contraction of "mister". One example you could use is Mr. Rogers. He is not "master" Rogers, he is "mister" Rogers. Hope this helps! :)

Right. “Mister”

The abbreviation "Mr." is actually a contraction of the word "mister". In formal English, "Mr." is used as a title before a man's name. The abbreviation "Mr." originated from the word "master," but over time, it evolved to become a separate title. If you ever wonder about the origin of a word or phrase, it can be helpful to consult a reliable etymology dictionary or do some research online.