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"enclosure" is also used as a crossword clue. If that's what you saw, the answer is often pen (3 letters).
Definitions
the act of enclosing something inside something else
Word origin
From Middle English enclosure, from Old French enclosure, from enclore, from Latin inclūdere, inclūdō, from in- (“in”) + claudō (“to shut”), ultimately from Proto-Indo-European *kleh₂u- (“key, hook, nail”). Alike to inclusion.
Used in a sentence
“There was an enclosure with the letter — a photo.”
“Mr Carlyle cut open the envelope, glanced at the enclosure, and in spite of his disappointment could not restrain a chuckle.”
“The enclosure of a photo with your letter is appreciated.”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Pen, perhaps”9 letters
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