knife sharpener
A tool or device for sharpening kitchen knives.
See also: 研ぎ器 (とぎき)
I used a knife sharpener to restore the sharpness.
A general sharpener; 包丁研ぎ器 specifically sharpens kitchen knives.
Compound of 包丁 (kitchen knife), 研ぎ (sharpening, from 研ぐ), and 器 (device).