Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
sharpen [ˈʃɑːpn] vt (stick etc) заостря́ть (заостри́ть perf) (pencil, knife) точи́ть*(поточи́ть*perf) (fig, appetite) уси́ливать (уси́лить perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: