whetstone, grind, sharpen, whet, encourage
厲 centers on the idea of a whetstone: a tool for grinding and sharpening blades. By extension, it can mean to encourage or spur someone on, as if sharpening their resolve.
厲 combines 厂 (cliff) with 萬 (scorpion), but the historical origin is uncertain. The modern form may have been used phonetically to represent a whetstone or grinding action.
Under the cliff (厂), a scorpion (萬) drags its stinger across a stone to sharpen it. The grinding action becomes a whetstone, and the sharpening motion suggests encouraging someone to be sharper.
For レイ, picture a ray of light hitting the whetstone under the cliff: ray -> レイ, and the light helps you see the sharpening process.