1540s, "to cut with a stroke of a blade or whip;" 1650s, "to strike violently," perhaps from French esclachier "to break," variant of esclater "to break, splinter" (see slat). Meaning "to clear land" (of trees) is from 1821, American English. In reference to prices, it is attested from 1906. Related: Slashed; slashing. Slash-and-burn for a method of clearing forest for cultivation is from 1919.
"a cutting stroke with a weapon," 1570s, from slash (v.); sense of "slit in a garment" is from 1610s; that of "open tract in a forest" is first attested 1825, American English. As a punctuation mark in writing or printing, it is recorded from 1961.