ICAO Annex 10, Volume II
5.2.1.5.8 The following words and phrases shall be used in radiotelephony communications as appropriate and shall have the meaning ascribed hereunder:

ACKNOWLEDGE “Let me know that you have received and understood this message.”
APPROVED “Permission for proposed action granted.”
BREAK “I hereby indicate the separation between portions of the message.” (To be used where there is no clear distinction between the text and other portions of the message.)
BREAK BREAK “I hereby indicate the separation between messages transmitted to different aircraft in a very busy environment.”
CANCEL “Annul the previously transmitted clearance.”
CHECK “Examine a system or procedure.” (Not to be used in any other context. No answer is normally expected.)
CLEARED “Authorized to proceed under the conditions specified.”
CONFIRM “I request verification of: (clearance, instruction, action, information).”
CONTACT “Establish communications with...”
CORRECT “True” or “Accurate”.
CORRECTION “An error has been made in this transmission (or message indicated). The correct version is...” DISREGARD “Ignore.”
HOW DO YOU READ “What is the readability of my transmission?”
I SAY AGAIN “I repeat for clarity or emphasis.”
MAINTAIN “Continue in accordance with the condition(s) specified” or in its literal sense, e.g. “Maintain VFR”.
MONITOR “Listen out on (frequency).”
NEGATIVE “No” or “Permission not granted” or “That is not correct” or “Not capable”.
OVER “My transmission is ended, and I expect a response from you.”
OUT “This exchange of transmissions is ended and no response is expected.”
READ BACK “Repeat all, or the specified part, of this message back to me exactly as received.”
RECLEARED “A change has been made to your last clearance and this new clearance supersedes your previous clearance or part thereof.”
REPORT “Pass me the following information...”
REQUEST “I should like to know...” or “I wish to obtain...”