I know that Mr. is short for Mister and Mrs. is short for Mistress. Is there any comparable way to abbreviate "Master" that is distinguishable from Mister? Or would it just be Mr. again?
Some airlines' tickets/boarding-passes use MSTR, e.g. from this travel website ...
MISS = Girl under 12 years,
MSTR = Boy under 12years,
INF = Under 2 years.
Please advise in special request, if you have flexible date
At one time at least, according to Wikipedia:
"Mstr" is [...] a prefix for boys on the UK Passport Service online application form. — Wikipedia
... however when I checked the UK website today, its current online form has a selection option with Master rather than Mstr! Note: the title does not appear on actual passport document, to avoid confusion I guess!
Update 13/Nov/2019: See https://travel.stackexchange.com/questions/149483/why-do-airline-tickets-have-titles-in-addition-to-names/149534#149534 which shows MSTR in use today on British Airways booking system.
a. Used formerly as a title for a man holding a naval office ranking next below a lieutenant on a warship.
b. Used as a title for a man who serves as the head or presiding officer of certain societies, clubs, orders, or institutions.
c. Used as a title for any of various male officers having specified duties concerning the management of the British royal household.
d. Used as a courtesy title before the given or full name of a boy not considered old enough to be addressed as Mister.
e. Archaic Used as a form of address for a man; mister.
Assuming you're not referring to an academic "Master" of some sort, but rather the honorific you might apply to a child before they turn 18 and gain the Mr. or Miss/Ms./Mrs. title, Master should be used in its entirety without abbreviation.