We found 20 dictionaries that define the word attn:

General (15 matching dictionaries)

1. attn: Merriam-Webster
2. attn: Oxford Learner's Dictionaries
3. attn: American Heritage Dictionary of the English Language
4. attn: Collins English Dictionary
5. Attn, attn: Wordnik
6. attn: Wiktionary
7. Attn: Webster's New World College Dictionary, 4th Ed.
8. attn: Infoplease Dictionary
9. attn, attn: Dictionary.com
10. Attn: Wikipedia, the Free Encyclopedia
11. attn, attn: TheFreeDictionary.com
12. attn: Longman Dictionary of Contemporary English
13. attn: Merriam-Webster

Computing (1 matching dictionary)

14. BABEL: Computer Oriented Abbreviations and Acronyms (No longer online)

Miscellaneous (2 matching dictionaries)

15. ATTN: Acronym Finder
16. AbbreviationZ (No longer online)

Slang (1 matching dictionary)

17. ATTN: Urban Dictionary

Tech (1 matching dictionary)

18. Explosives (No longer online)

Definitions from Wiktionary ( ) ▸ noun:  Abbreviation of attention, used as a heading in letters to indicate for whom the letter is intended. [(uncountable) Mental focus.] Similar: attention, atten, attent, paying, payin, addy, focus, snet, atty., adm, more... Opposite: distraction, inattention, disregard, neglect ▸ Words similar to attn ▸ Usage examples for attn ▸ Idioms related to attn ▸ Wikipedia articles (New!) ▸ Popular adjectives describing attn ▸ Words that often appear near attn ▸ Rhymes of attn ▸ Invented words related to attn