sharpen
/ˈʃɑ:pən; `ʃɑrpən/ v[I, Tn]
(cause sth to) become sharp （使某物）锋利, 尖锐, 陡峭, 清晰, 强烈
The tone of his letters has sharpened (ie become less friendly) recently. 他最近来信的口气变得刻薄起来.
sharpen a pencil 削铅笔
This knife needs sharpening. 这把刀要磨一下.
This incident has sharpened public awareness of the economic crisis. 这件事提高了公众对经济危机的认识.
sharpen sb's wits, ie make sb more mentally alert 使某人更机智.