RA      
 adjective  anatomy specialized uk/ɑː ˈeɪ/ us/aːr ˈeɪ/
 桡动脉(radial artery的缩写)
abbreviation for radial artery: the artery (= large blood vessel) that goes from below the elbow to the palm of the hand
 RA      
noun [ C ]  anatomy specialized uk/ɑː ˈeɪ/ us/aːr ˈeɪ/
 右心房(right atrium的缩写)
abbreviation for right atrium: the right upper chamber (= space) of the heart