Definition of "ack" []

• A in RAF phonetic alphabet (noun)
• Acknowledgment signal (noun)
• Acknowledged (interjection)
• Expressing distaste, alarm, or trepidation. (interjection)

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• "Yes, please go see Kiki - it is very good, even in English ack! but if you can't get the sub, the dub is not the worst."
• "Nicholas Baker of Louisville, Kentucky, called that classification into question, suggesting that the origin of ack-ack is German acht acht ` 8.8, 'from the designation for the weapon by its bore diameter in centimeters."
• "I do not know if there is any connection between this and the British term ack-ack."