This root appears in the “Quendi and Eldar” essay from 1959-60 with the sense “walk, go, proceed, travel” (WJ/360). Its derivatives S. Edhel “Elf”, Q. †Eldo blended with Elda “Elf”, both originally with the sense “one who goes” (✶edelō): those who left lake Cuiviénen to travel to Valinor. It is also the basis of several words meaning “to go”: T. delia- and Q. lelya-.
Many of Quenya derivatives of this root actually derive from an inversion √LED of the original √DEL. According to the “Quendi and Eldar” essay, this inversion only occurred in Quenya (WJ/363). In earlier writings like The Etymologies, however, ᴹ√LED “go, fare, travel” was the basic root in all languages. It seems that Tolkien revised ᴹ√LED >> √DEL¹, preserving √LED only as a Quenya variant. The strongest sign of this change was Tolkien’s consistent alteration of N. Eledh >> S. Edhel.
This leave open the question of what happened to the other non-Quenya derivatives of ᴹ√LED, such as S. edlen(n) “exile”. It is possible that they were transfered to √LEN “way”, which was the basis for S. lembas “way bread”.