The OED considers the etymological origin of the verb pour unknown, though they believe the ME form is likely derived from AN. The DMF considers purer#2 a subsense of purer#1 and thus includes both together in their entry, as do the DEAF, who define the word as 'purifier, nettoyer, égoutter'. The sense of 'pour' does not appear to be one of the sense of ML purare (DMBLS 2580b). We follow the OED and have given it a separate entry as it is unclear if purer² shares an etymology with purer¹.