adjective/o pɛʁ/
working for food and housing
“Sylvie Rogron fut envoyée à cent écus de pension en apprentissage rue Saint-Denis, chez des négociants nés à Provins. Deux ans après, elle était au pair : si elle ne gagnait rien, ses parents ne payaient plus rien pour son logis et sa nourriture. Voilà ce qu’on appelle être au pair, rue Saint-Denis.” — Sylvie Rogron was sent (with six hundred francs for her board) as apprentice to certain shopkeepers originally from Provins and now settled in Paris in the rue Saint-Denis. Two years later she was "at par" as they say; she earned her own living; at any rate her parents paid nothing for her. That is what is called being "at par" in the rue Saint-Denis.