From Longman Dictionary of Contemporary Englishweak-willedˌweak-ˈwilled adjective DECIDEsomeone who is weak-willed does not do something difficult that they had intended to do OPP strong-willed
Examples from the Corpus
weak-willed• Call me a weak-willed sentimentalist, but I liked it damn it, I liked it!• He had four children, two parents, and a weak-willed sister.• It was not a step for a weak-willed woman to take. 