Entry 1 sense Webster, 1913 Masterfully · Mas·ter·ful·ly · IPA /ˈmæstɚf(ʊ)li/ 01 adv. In a masterful manner; imperiously. 1. In a masterful manner; imperiously. “A lawless and rebellious man who held lands masterfully and in high contempt of the royal authority.” — Macaulay.