Proverbs 27:17

sharpeneth This has been understood to mean exasperates. Comp. Mine enemy sharpeneth his eyes upon me, Job 16:9 (where, however, the Hebrew word is different). But, as it is a friendthat is spoken of here, it is better to take the proverb in a good sense. See for illustrations, 1 Kings 10:1; 1 Kings 10:3; Acts 28:15.

The effect, however, is mutual, not like that of the whetstone to which Horace compares the critic,

acutum

Reddere quæ ferrum valet, exsors ipsa secandi.

De Art. Poet. 304, 5.