To fasten or secure something firmly; to make fast or secure.
From en- (to cause to be) plus 'fasten,' which comes from Old English 'fæst' (firm, fast). The en- prefix adds emphasis to the act of securing.
Words like 'enfasten' show the power of the en- prefix—you can potentially add it to almost any adjective or noun and make it a verb meaning 'to cause [thing] to be [adjective]'!
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