An unglossed root in The Etymologies of the 1930s with derivatives like N. gath “cavern” and N. gador “prison, dungeon” (GAT(H)), so probably meaning something like “✱cave”. Its most notable derivative was N. Doriath “Land of the Cave”. But later on in this same entry, Tolkien added Doriathrin words Dor. gad “fence” and Dor. argad “outside the fence”, indicating a conceptual shift in the meaning of this root. Indeed, in later versions of The Silmarillion, S. Doriath was translated “Land of the Fence” containing the element S. iath “fence” (WJ/370, 378), so most likely ᴹ√GAT(H) “✱cave” was abandoned.
Middle Primitive Elvish
gat
root. *catch
gat(h)
root. *cave
An unglossed root in The Etymologies of the 1930s with derivatives like ᴹQ. atsa “claw, catch, hook” and N. gad- “catch” (Ety/GAT), so probably meaning something like “catch”. It is not clear whether this root remained valid in Tolkien’s later writing.