cha.dah describes the sharpening of one person by another through the iron-on-iron comparison in Proverbs 27:17.

The attested use describes sharpening through a reciprocal comparison: Proverbs 27:17 sets iron sharpening iron alongside one person sharpening another.

1. Sharpening by comparison · dominant

   In Proverbs 27:17, the two Hiphil imperfect masculine singular forms occur in the comparison between iron and iron and between one person and another; the APB renders the verse, "As iron sharpens iron, so one person sharpens another."

   Proverbs 27:17

In the Anselm Project Bible: In Proverbs 27:17, the APB presents the comparison with "sharpens" for both iron and the person-to-person parallel.