An adjective for “flat” in The Etymologies of the 1930s under the root ᴹ√DAL of the same meaning (Ety/DAL).

Neo-Sindarin: Given the revision of N. dalath to S. talath “plain”, I would adapt this word as ᴺS. talu as suggested in Hiswelókë’s Sindarin Dictionary (HSD). I would use this word for “flat” in its most general sense, as opened to laden which means “flat (and wide)” with an implication of a wide open and level expanse, mostly used in describing landscapes.