• IPA: /æk/

ack (plural acks)

1. (military, now historical) The letter A as used in signalling and other types of communications.
   • 1929, Frederic Manning, The Middle Parts of Fortune, Vintage, published 2014, page 173:

     They had to begin at the beginning: learning the Morse code, flag-wagging, a succession of acks, and practice on the buzzer.

2. (data communications) acknowledgment signal

• (antonym(s) of “data communications”): nack, nak

ack (acks, present participle acking; simple past and past participle acked)

1. Alt form of ACK.

1. (radio communications) acknowledged

Imitative.

1. Expressing distaste, alarm, or trepidation.

ack (plural acks)

1. (networking) An acknowledgement either of a packet or a message received from a network.

• NAK

ack (acks, present participle acking; simple past and past participle acked)

1. (networking) To acknowledge a packet or a message received from a network.