Longman Dictionary of Contemporary English
Wiktionary
n. a small bedroom in a house, often used for storage.
Usage examples of "box room".
It was an old Alpine rope of mine put away in the box room with my climbing kit.
She went into the box room and looked through the boxes until she found a suitable hat: navy with a white petersham ribbon.
Glittering blades and shiny scabbards were exploding out of the little box room where he stored his collection, protruding through the door as if some huge metallic hedgehog was trying to break out from hibernation there.
No one in five other bedrooms, nor in the box room no one in the bathrooms, no one in the plum and pink lushness of Malcolm's own suite.
The boy turned to the box room door and set the palm of one hand against it.
I open the skylight in the toilet and the one in the box room to get a through draught and stand there shivering until I pull on my dressing-gown, feeling mightily pleased with myself.