noun, feminine/ɡaʁ.sɔ.njɛʁ/plural: garçonnières
bachelor pad; an attic, usually accessed from the front porch, where the male children of a household traditionally slept
“Des passants nous épieraient. Je ferais semblant de ne pas les voir. Je recevrais ma maîtresse dans une garçonnière au rez-de-chaussée d’une maison neuve.” — Passers-by would spy on us. I would pretend not to see them. I would see my mistress in a bachelor flat on the ground floor of a new house.
From garçon + -ière.