Sentence:  The beaver trap is a <WSD>deadfall</WSD> of considerable weight, nicely adjusted over the animal's road or track, frequently on a dam. ... The animal passing under the <WSD>deadfall</WSD> has to step on a little stick raised an inch or two above the ground, and this brings down the <WSD>deadfall</WSD> on its back. 
Meaning of the word marked with <WSD> tags:  A kind of trap for animals, consisting of a heavy board or log that falls on to the prey.