Au pair

A young foreigner who remains with a family as a surrogate family member, takes care of some of the house work such as baby-care etc. and in turn gets boarding, food and other amenities of being with a family, plus the learning of local language and culture.

Comes from the French au pair, meaning "on par" or "equal to". So the relationship with the person is on equal terms, he/ she is member of the family not a servant. Though the relationship is supposed to be temporary, its expected that they will remain in touch and on good terms years after the 'au pair' has left for his home country.

Example
One memory of that visit was of Jackie, the plump and pretty au pair at 18 Queens Road, who was huggable and on whom I had a crush.
Two Lives, by Vikram Seth