flounder

Despite the fact that flounder is a relatively common English verb, its origins in the language remain obscure. It is thought that it may be an alteration of an older verb, founder. To founder is to become disabled, to give way or collapse, or to come to grief or to fail. In the case of a waterborne vessel, to founder is to sink. The oldest of these senses of founder, "to become disabled," was also used, particularly in reference to a horse and its rider, for the act of stumbling violently or collapsing. It may have been this sense of founder that later appeared in altered form as flounder in the sense of "to stumble."