What is the significance of the title with respect to the short story, "The Lumber Room"?

The title of Saki's short story, "The Lumber Room" is significant because this forbidden room represents the self-appointed aunt's lack of imagination and appreciation for creativity, all of which Nicholas possesses. The boy's ability to find the key and enter into this room represents his victory over his aunt's petty dullness.

After he is punished for his subversive prank of tricking the obtuse aunt about a frog being in his morning bowl of bread-and-milk, Nicholas...

The title of Saki's short story, "The Lumber Room" is significant because this forbidden room represents the self-appointed aunt's lack of imagination and appreciation for creativity, all of which Nicholas possesses. The boy's ability to find the key and enter into this room represents his victory over his aunt's petty dullness.

After he is punished for his subversive prank of tricking the obtuse aunt about a frog being in his morning bowl of bread-and-milk, Nicholas is sentenced to remain home while his boy and girl cousins are afforded the privilege of going to the beach. And, because he is in "disgrace," Nicholas is forbidden entrance into the gooseberry garden. Now, because Nicholas could enter this garden by one of two doors and hide in the "masking growth" of vegetables, the aunt decides that she will have to keep the garden under her surveillance: 

...she spent an hour or two in trivial gardening operations among flower beds and shrubberies, whence she could watch the two doors that led to the forbidden paradise. She was a woman of few ideas, with immense powers of concentration.

While she is thus occupied, Nicholas sneaks off to the lumber room for which he has discovered the key. He opens the door and enters into "an unknown land" filled with artistic items such as a tapestry which tells the story of a hunter and his dogs, who pursue a stag. There several other interesting items are stored, among them a book of delightful pictures of resplendent birds.

After a while, Nicholas hears a shrill cry from his aunt, who has fallen into a water tank in the gooseberry garden. Again, he foils her as she cries for rescue, but he cleverly reminds her that he has been forbidden to enter this garden. So, she must remain in this embarrassing position until a kitchen maid needs vegetables from this garden and hears her cries.

That evening, it is an aunt who sits in "frozen muteness" at supper because the cousins have not enjoyed their day, either. Only the silence of Nicholas contains bemusement as he wonders whether the hunter and his hounds will escape while the wolves devour his wounded stag in the lumber room.