Translation guide
The act of making something sharp, such as a blade or a pencil. In Japanese, the verb used depends on the object being sharpened.
To make a blade sharp by grinding or honing.
General verb for sharpening blades, especially knives. Also used for polishing rice.
Sharpen a kitchen knife.
Alternate kanji for 研ぐ, specifically for sharpening on a whetstone. Less common in everyday writing.
刀を砥ぐ。
Sharpen a sword.
To sharpen to a fine edge; also used metaphorically for sharpening one's senses or skills.
感覚を研ぎ澄ます。
Sharpen one's senses.
To make a pencil point sharp using a sharpener or knife.
To sharpen a pencil by shaving off wood. Also means to shave, whittle, or cut down (e.g., budget).
鉛筆を削る。
Sharpen a pencil.
To use a pencil sharpener. 鉛筆削り is the noun for 'pencil sharpener'.
鉛筆削りを使って鉛筆を削る。
Sharpen a pencil with a pencil sharpener.
To sharpen a tool like a chisel or plane blade.
To improve or hone an ability, sense, or mental acuity.
To polish, refine, or improve a skill. Literally means to polish a surface, but widely used for skills.
技術を磨く。
Sharpen one's skills.
To sharpen to a fine edge; used for senses or mental focus.
To forge, train, or discipline. Used for physical or mental strengthening.
Use 研ぐ (とぐ) for blades (knives, swords, tools) and 削る (けずる) for pencils. Using the wrong verb sounds unnatural.
包丁を削る（不自然）
Sharpen a knife (unnatural, use 研ぐ)
The English word 'sharpening' cannot be directly translated as a single noun in most contexts. Use the appropriate verb phrase instead.
神経を研ぎ澄ます。
Sharpen one's nerves / be on high alert.
頭を鍛える。
Sharpen one's mind.