sharp + -en

1. make or become sharp or sharper:

〈物〉を鋭くする, 研ぐ, とがらせる

e.g. with object : she sharpened her pencil

〈刃物･鉛筆などが〉鋭くなる

e.g. no object : her tone sharpened.

2. (sharpen up or sharpen something up) improve or cause to improve:

〈技術〉を磨く, 高める, 〈感覚･理解力〉を鋭敏にする(up)

e.g. they've got to sharpen up in front of the goal

e.g. students will sharpen up their reading skills.

3. with object Music British raise the pitch of (a note) by a semitone.