Old English fæstnian "make fast, make firm, fix, secure," also "ratify, betroth, confirm," from Proto-Germanic *fastinon "to make firm or fast" (cognates: Old Frisian festnia "to make firm, bind fast," Old Saxon fastnon, Old High German fastnion, German festnen, Old Norse fastna "to pledge, betroth"), from PIE *fast "solid, firm" (see fast, adj.). Related: Fastened; fastening.