A verb for “climb” appearing in a rejected note from the late 1960s, probably a combination of am “up” and RAT “find a way”.
Neo-Sindarin: I would retain ᴺS. amrad- for purposes of Neo-Sindarin, since it is the only attested Sindarin verb with this meaning.
This name was used to two distinct tracks. The first is a road crossing the Greenway between the Barrow-downs and the South Downs (UT/348) and running from ancient Fornost down to Tharbad (TI/305). The second is the pass from Rivendell over the Misty Mountains translated by Christopher Tolkien as “long climb” (UT/271, 278 note #4). This name is a combination of and “long” and rath “(climbing) street”.
Conceptual Development: The road crossing the Greenway was first mentioned in Lord of the Rings drafts with the name N. Amrath (perhaps “✱up-course”), soon changed to Andrath (TI/72, 79). It also appeared on draft maps for the Lord of the Rings (TI/298, 305), but the name did not appear in the published book or its maps. The road was mentioned again in Tolkien’s private essays on “The Hunt for the Ring” (UT/348). I believe Tolkien intended name this road crossing the Greenway to mean something like “✱Long Street or Long Course”.
In a different essay on “The Disaster at Gladden Fields”, the name Andrath was applied to the “high-climbing pass” over the Misty Mountains [named only in this essay], the pass that Bilbo and the Dwarves used in the Hobbit, more fully named Cirith Forn en Andrath; Christopher Tolkien suggested in this second instance it meant “long climb” (UT/271, 278 note #4).