Capable of acting as a proton donor (strongly or weakly acidic as a Brønsted acid). The term is preferred to the synonym protic or the more ambiguous expression acidic by itself.
Source:
PAC, 1983, 55, 1281. 'Glossary of terms used in physical organic chemistry' on page 1348 (https://doi.org/10.1351/pac198355081281)