plein·air·ism \plāˈna(a)ˌrizəm\noun orplein·air·isme\plenerēs(mə), -ēz(mə), -s(mə), -z(mə)\ (-s) Etymology: French pleinairisme, from plein air + -isme -ism : the study, action, or product of plein air painting; specifically: the plein air art movement in France