Raphah (רָפָה) means to sink down, relax, let go of tension, grow slack, or cease striving. It appears about 46 times in multiple stems. In the Qal, it can mean to become weak or limp; in the Hiphil, "to let go," "to release," or "to set at rest." Do not confuse with rapha (H7495, to heal) — a similar-sounding but distinct root.
The most famous occurrence is Psalm 46:10: "Be still [raphah] and know that I am God" — literally "let go / relax / cease striving and know that I am God."
In a culture of striving, proving, and performing, raphah is the counterintuitive word of the LORD: stop fighting. Release your grip. The context of Psalm 46:10 is not quiet contemplation but cosmic conflict — nations are in uproar, kingdoms tottering, the earth itself is changing (vv.1-9). Into that chaos, God commands: raphah. Not because the battle isn't real, but because HE is fighting it.
This connects to the concept of Sabbath rest: one day in seven, Israel was commanded to raphah — to release the illusion of self-sufficiency and acknowledge that God is the provider. Hebrews 4 draws this out: the Sabbath rest of God (Gen. 2:2) prefigures the eternal rest of those who trust in Christ. Spiritual maturity involves learning the posture of raphah — releasing control to the Sovereign who holds all things.