Is "adelphi" really a Greek word?

[Tripp]

I sometimes run across the word adelphi, generally as part of the name of a purportedly Christian organization or institution (e.g., Adelphi Christian Academy was the name of a private school that some kids in my church attended). But is this a bona fide Greek word form?

Is it an attempt to transliterate the nominative plural adelphoi as it may be pronounced in some pronunciation schemes?

Is it part of a non-Koine (or at least non-biblical) declension that I'm not familiar with?

Could it be a Latin corruption of a Greek word?

Or is it just plain wrong?