Sentence:  The planing-machine, on the contrary, uses revolving knives, which make a succession of little <WSD>gouges</WSD> in the wood; these <WSD>gouges</WSD>, which would otherwise leave the surface very irregular, are made to leave it tolerably smooth by following one another so closely that the <WSD>gouges</WSD> become one long <WSD>gouge</WSD> or cut; [...] 
Meaning of the word marked with <WSD> tags:  A cut or groove, as left by a gouge or something sharp.