The primary verb for blessing, over 330 times. Means to endue with power for success, prosperity, longevity. When God blesses, He bestows favor; when humans bless God, they praise.
First occurrence: Gen 1:22 — God blesses creatures. By Gen 12:2-3, blessing becomes vehicle of redemption. Psalms overflow with barak toward God. Creates theological rhythm: God blesses down, humans bless up and laterally.
Euphemistically can mean 'curse' (Job 1:5) — scribal convention. Piel intensive form is most common. Connection to berek (knee) suggests posture of supplication.