Sentence:  "This wall is badly built," he went on in a careless tone; "look, there is another space there at the back;" and he actually came up to it and held the lantern close to the <WSD>airhole</WSD> in such fashion that its light shone through into Jess's eyes and nearly blinded her. 
Meaning of the word marked with <WSD> tags:  A hole provided for ventilation or breathing.