rh-

consonantal digraph, an initial sequence used in Latin (and thus in English words from Latin) to represent Greek initial aspirated r-. The medial Greek form of it usually is represented by -rrh-, as in catarrh, diarrhea, hemorrhage, myrrh, Pyrrhic. As it was pronounced as simply "r" in Middle English (as in Old French and Spanish), the -h- tended to be dropped in spelling but was restored in early Modern English with the classical revival.