A word for “shadow” but more accurately an area of “dim light”, since it was “not for the shadows of actual objects or persons cast by sun or moon or other lights” (VT42/9) but was used “in the sense of dim light, owing to cloud or mist, or in deep valleys” (UT/261). A cast shadow would be morchant “(lit.) dark shape” (VT42/9). Gwath was derived from the root √WATH.
Conceptual Development: N. gwath “shade” appeared in The Etymologies of the 1930s, already with the derivation given above (Ety/WATH).
The root ᴹ√WATH “shade” first appeared in The Etymologies of the 1930s with derivatives like N. gwath of the same meaning (Ety/WATH). Primitive ✶wath “shadow” was mentioned in notes on Words, Phrases and Passages from the Lord of the Rings from the late 1950s as the basis for S. gwath (PE17/41), and primitive root √WATH appeared in notes on The Rivers and Beacon-hills of Gondor from 1967-69, again as the basis for S. gwath and similar words like S. gwathren “shadowy, dim” and Q. vasar “veil”, the latter from extended form waþar [√WATHAR] which was apparently the only survival of the shorter root in Quenya (VT42/9-10). This extended root might also be the basis for the (archaic?) region name Q. Avathar “Shadows” from The Silmarillion (S/73-4; MR/284).