From The Collaborative International Dictionary of English v.0.48 [gcide]:
Waiting \Wait"ing\,
a. & n. from Wait, v.
[1913 Webster]
In waiting, in attendance; as, lords in waiting. [Eng.]
Waiting gentlewoman, a woman who waits upon a person of
rank.
Waiting maid, Waiting woman, a maid or woman who waits
upon another as a personal servant.
[1913 Webster]