Old English strengþu, strengð "bodily power, force, vigor, firmness, fortitude, manhood, violence, moral resistance," from Proto-Germanic *strangitho (cognates: Old High German strengida "strength"), from PIE *strenk- "tight, narrow" (see string, n.), with Proto-Germanic abstract noun suffix *-itho (see -th(2)). Compare length/long. From the same root as strong,