Fasten

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Old English fæstnian ‘make sure’, also ‘immobilize’, of West Germanic origin; related to fast1.

wiktionary

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From Middle English fastenen, from Old English fæstnian, from Proto-West Germanic *fastinōn(“to secure, fasten”). Equivalent to fast +‎ -en.

etymonline

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fasten (v.)

Old English fæstnian "make fast, make firm, fix, secure," also "ratify, betroth, confirm," from Proto-Germanic *fastinon "to make firm or fast" (source also of 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.