missive has definitions from the field of writing
1
[ noun ] (writing) a written message addressed to a person or organization

Synonyms

letter

Examples

"wrote an indignant letter to the editor"

Used in print

(Bell I. Wiley, "Home Letters of Johnny Reb and Billy...)

Still another , annoyed by the brevity of a recently received missive , wrote : `` Yore letter was short_and_sweet , jist like a roasted maget '' .

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