in waiting

from The Collaborative International Dictionary of English v.0.48

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]