R1 Syllabification: (R)Pronunciation: /är/ (also r)Translate R | into French | into German | into Italian | into Spanish Definition of R noun (plural Rs or R's) the eighteenth letter of the alphabet. denoting the next after Q in a set of items, categories, etc.. Phrases the R months the months with R in their names (September to April), considered to be the season for eating oysters. the three Rs reading, writing, and arithmetic, regarded as the fundamentals of learning. R in other Oxford dictionaries Definition of R in the British & World English dictionary