Why not use a different phrase, which has no element of possible confusion attached to it, instead ?
"Clear" in this context means having "clearance" (authorization) for an action:
(Merriam-Webster)
clearance noun clear·ance \ˈklir-ən(t)s\
1: an act or process of clearing: as
f : authorization for an aircraft to proceed especially with a specified action <clearance to land>
When ATC clears you for an IFR flight from JFK to LAX, that does not mean that at that very moment all airspace between NY and Los Angeles is physically clear for your flight. Rather, it is only an authorization for you to proceed according to the clearance.
Similarly, the phrase "number two, cleared to land" does not mean that the runway at that very moment is physically clear, but instead is an authorization to land after the preceding aircraft.