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"fasten" is also used as a crossword clue. If that's what you saw, the answer is often attach (6 letters).
Definitions
make tight or tighter
Word origin
From Middle English fastenen, from Old English fæstnian, from Proto-West Germanic *fastinōn (“to secure, fasten”). Equivalent to fast + -en.
Used in a sentence
“The sailor fastened the boat to the dock with a half-hitch.”
“Fasten your seat belts!”
“Can you fasten these boards together with some nails?”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Attach securely”6 letters
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