A History of Short Words

From the New York Times Crossword Puzzle

ATTN

Wed, 27 Jul '22
Abbr. before a name on an envelope
Sun, 16 Jan '22
Memo abbr.
Thu, 13 Jan '22
Subject line abbr.
Sun, 9 Jan '22
Subj. line heading
Mon, 14 Jun '21
Abbr. for routing of mail