Entry 2 senses · 2 variants Webster, 1913 Weakly /wēk'-lē/ approx. · Weak·ly · IPA /ˈwiːkli/ adv. a. 01 adv. In a weak manner; with little strength or vigor; feebly. 1. In a weak manner; with little strength or vigor; feebly. 02 a. Not strong of constitution; infirm; feeble; as, a weakly woman; a man of a weakly constitution. 1. Not strong of constitution; infirm; feeble; as, a weakly woman; a man of a weakly constitution.