1520s, "bring to an edge or point," from sharp (adj.) + -en (1). Related: Sharpened; sharpening. Old English verb scearpian meant "to score, scarify;" also compare scearpung "scarifying." To sharpen (one's) pencil "prepare to get to work" is from 1957, American English.
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Definitions of sharpener from WordNet
any implement that is used to make something (an edge or a point) sharper;