Sentence:  We tiptoed into the house, up the stairs and along the hall into the room where the Professor had been spending so much of his time. 'Twas locked, of course, but the Deacon man got a big bunch of keys out of his pocket and commenced to putter with the <WSD>lock</WSD>. 
Meaning of the word marked with <WSD> tags:  Something used for fastening, which can only be opened with a key or combination.