A noun in The Etymologies of the 1930s glossed “prison, dungeon” derived from the ᴹ√GAT(H) (Ety/GAT(H)).

Neo-Sindarin: Another derivative of this root was N. gath “cavern”, also appearing as the initial element of the name N. Doriath “Land of the Cave”. In later writings S. Doriath was redefined as “Land of the Fence” with final element S. iath “fence” (WJ/370), so the root ᴹ√GAT(H) was probably abandoned. However, I think gador “prison” may be salvaged as a derivative of the root ᴹ√GAT “catch” instead.