WordNet (r) 3.0 (2006):

au pair girl
    n 1: a foreign girl serving as an au pair

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "au pair girl":
   abigail, amah, ayah, betweenmaid, biddy, chambermaid, chaperon,
   companion, cook, duenna, femme de chambre, fille de chambre,
   gentlewoman, girl, handmaid, handmaiden, hired girl, housemaid,
   kitchenmaid, lady-help, lady-in-waiting, live-in maid,
   live-out maid, maid, maidservant, nursemaid, parlormaid,
   scullery maid, servant girl, servitress, soubrette, tweeny,
   upstairs maid, waiting maid, wench