When should a pilot use the word "takeoff?" I've been taught before that the word "takeoff" should only be used when reading back a clearance, and that when requesting a clearance pilots should advise "ready" or "ready for departure."

Here's the really critical point to the question. I've always believed that the word "takeoff" should only be used when reading back a clearance for such an action. Not when requesting a clearance for that action.

I've also heard it taught that this is true only for IFR flights but it's okay to ask for a clearance with the word "takeoff" when VFR. I don't see why the difference between VFR or IFR flight would be a factor here.

Has the ICAO, FAA or any other controlling organization released any written guidance on radio communications that covers this procedure?
The word "Takeoff" should only be used when clearing somebody for takeoff, acknowledging your takeoff clearance, or cancelling/acknowledging a cancelled takeoff clearance.

"Departure" should be used in all other circumstances, and as far as I'm aware whoever told you you could use the word Takeoff for VFR was wrong.

Anybody saying the word "takeoff" intends for an aircraft to enter, accelerate along, and then leave a runway in the immediate future: never anything else. Anybody saying otherwise should be immediately directed to the Wikipedia article for the Tenerife 747 disaster.