We don't have synonyms for rhamadan yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are ramadan, hamadan and rhamadhan.
(n) :
Archaic form of Ramadan. [(Islam) The holy ninth month of the Islamic lunar calendar, during which Muslims fast between the break of dawn until sunset; they also refrain from drinking liquids, smoking and having sexual relations.]
(n) :
Archaic form of Ramadan. [(Islam) The holy ninth month of the Islamic lunar calendar, during which Muslims fast between the break of dawn until sunset; they also refrain from drinking liquids, smoking and having sexual relations.]