The Hebrew verb athar (עָתַר) means to pray, entreat, or supplicate — with the sense of an urgent, fervent, or pleading prayer. It appears about 20 times in the OT, concentrated in the Exodus plague narratives.
Athar is the word used repeatedly in the plague narratives of Exodus: Pharaoh begs Moses to entreat the LORD (athar) to remove the plagues (Exodus 8:8–30; 9:28; 10:17). Moses prayed to God and God heard and removed the plague. This reveals a profound truth: even a pagan king knew that Moses had direct access to God. The word also appears in Genesis 25:21 — Isaac prayed (athar) to the LORD on behalf of his childless wife Rebekah. This single act of spousal intercession bore fruit: she conceived the twins Jacob and Esau. Athar is the prayer of desperation that moves heaven.