Go ahead. Go to Google and enter the word masteral. Or if you’re lazy, just click here. The first few pages all list sites coming from the Philippines or written by Filipinos.
I admit I may have used that word myself before, and today I’ve heard someone say it again. I don’t think I’ve heard that word uttered while living in the U.S. for more than 3 years now. Not surprisingly, today it was a fellow Filipino who said it.
I decided to look it up online, and I think I can safely say that this word is a purely Filipino concoction. It isn’t on the Merriam-Webster dictionary. Nor is it in the Oxford English Dictionary. It may not be an official word by the OED’s standards. Judging from the results from that Google search though, it is a word that is definitely in common use in the Philippines. It most definitely looks like applying the -al suffix in doctoral (which definitely is an official word), to master — hence, masteral. I’m sure linguists have a term for such type of word form. If I may follow the OED’s definition of doctoral, then:
masteral, a.
Of or belonging to one who has received the degree of Master.
Its use in the Philippines is such that even universities and government officials use the word as if it is an official English word. It may not belong to the OED, but if there’s such a thing as a Dictionary of Filipino English, it should definitely be in it. To be fair though, I’ve found at least one U.S. site that uses the word though I won’t be surprised if that site’s webmaster is a Filipino.