What word should be avoided unless in the tower/terminal environment?

In the context of air traffic control and communications, the word "takeoff" should generally be reserved for use in the tower or terminal environment. This is because "takeoff" has a specific meaning in aviation; it refers to the phase when an aircraft transitions from ground to air while departing from an airport. Using this term in a non-tower environment can lead to confusion regarding the aircraft's status, as it may not be clear whether an aircraft has already taken off, is about to take off, or is still on the ground preparing for departure.

Other terms like "climb," "ascend," or "departure" have broader uses and can be applied in various contexts outside the immediate tower or terminal environment without the same risk of miscommunication. For example, "climb" and "ascend" can refer to an aircraft gaining altitude at any point in its flight, regardless of whether it is still in the terminal area. "Departure" is also a more general term that can signify an aircraft leaving any airspace, and it doesn't inherently imply that the aircraft has already taken off. Therefore, restricting the use of "takeoff" to the tower/terminal environment helps ensure clarity and precision in communication among pilots and air traffic controllers.