The Hebrew noun akzeriyyuth (אַכְזְרִיּוּת) means "cruelty, fierceness, mercilessness" — the abstract noun form derived from akzar (H393) and akzari (H394). It names the quality or condition of cruelty itself, not just the act. This word appears only in Proverbs 27:4 in the Old Testament.
In Proverbs 27:4, wisdom compares the destructive power of chemath (wrath/fury) with the ultimate test: "Cruelty (akzeriyyuth) is overwhelming, and who can stand before jealousy?" The verse acknowledges that raw fury is bad enough — but cruelty combined with jealousy (or possessive wrath) becomes nearly irresistible to endure. The Bible's wisdom literature is not naive about human evil; it names and catalogs the darkest capacities of the fallen heart. This naming is itself a mercy — to identify evil is the first step toward fleeing it and seeking God's transforming grace.