As a verb miter

is to finish a material at an angle, frequently 45 degrees, or sometimes with some specific shape, so that it will fit up tightly against another piece of material, as with a picture frame.

As a noun miter

is an alternative spelling of lang=en.

As an abbreviation Mr is

an abbreviation of mister, a title used before the surname in theory, though not generally in practice, above some undefined social level, too old to be addressed as “Master”, not a knight or of some higher rank, and, in Britain though not in the United States, not entitled to be addressed as “Dr”.