From the Oxford Dictionary:
NOUN
1. chiefly North American, A cupboard or wardrobe, especially one tall enough to walk into
2. used to reveal a state of secrecy.....
ADJECTIVE
secret; covert
VERB
shut (someone) away, especially in private conference or study
ORIGIN
late Middle English (denoting a private or small room): from Old French, diminutive of clos 'closed' (see close1).