The compound adjective 'weak-willed' is a relatively modern English formation, built from two native Germanic elements. The first element, 'weak', originates from the Old English wāc, which carried meanings of pliability and lack of strength, both physical and moral. The second element derives from 'will', from Old English will, a central concept in Germanic thought denoting desire, intention, and firm resolve. The '-ed' suffix transforms it into an adjective describing possession. Thus, the literal construction "having a weak will" perfectly captures the modern psychological meaning of someone whose resolve or decision-making faculty is deficient and easily overcome.

Structure: weak (lacking strength) + willed (having a will) - weak: From Old English wāc (pliant, yielding, weak), of Germanic origin. In this compound, it functions as an adjective describing a quality of the noun 'will'. - willed: From the noun 'will' (Old English will, willa meaning desire, determination) combined with the past participle suffix '-ed', forming an adjective meaning 'having a will of a specified kind'.