BROTHER — a title of a clergyman of various religious orders in Spanish countriesThis absence from other dictionaries is surprising considering that the word is not uncommon in English. Here are some hit counts from Google, with Google's language settings restricted to English and Japanese:
"Fray Pedro" 657Some of the hits are spurious, of course, but a glance at a few pages of results confirms that "fray" is well established in this meaning in English. It's a surprising omission from the other dictionaries.
"Fray Juan" 1660
"Fray Garcia" 212
(January 4, 2003)