Two guesses in one: rhitidiadelfus
heard as rhitidiadelfus
spelled rhytidiadelphus
Rhytidiadelphus. The y stays and the ph stays.
What the ear did
The rh has survived here but the two Greek spellings inside the word have not. Whoever wrote this heard the word correctly and trusted the sound, which is the right instinct for English and the wrong one for a transliterated Greek compound.
R-H-Y-T-I-D-I-A-D-E-L-P-H-U-S
The full entry for rhytidiadelphus covers the name itself.