A word used in street-names in Minis Tirith, most notably Rath Celerdain “Lampwrights’ Street” (LotR/768) and Rath Dínen “Silent Street” (LotR/826). It was also an element in the (rejected) name Raith ’Ngorthrim “Paths of the Dead” (RC/526) and the river-name Rathlóriel “Golden-bed” (S/235), but the last of these may be a remnant of its 1930s meaning (see below). In the “Unfinished Index” of The Lord of the Rings Tolkien indicated that rath meant “street (in a city)” (RC/523, 551).
The most extensive description of this word appears in a 1968 discussion of the (possibly related) name Amroth which Tolkien said “is connected with a stem RATH meaning ‘climb’ - with hands and feet, as in a tree or up a rocky slope”. Regarding S. rath Tolkien said:
> Both Quenya and Lindarin also possessed a word ratta, which might be a derivative (by lengthening the medial consonant, a frequent device in Primitive Eldarin) from either ✱rattha or ✱ratta from the stem RAT ... It meant ‘a track’; though often applied to ways known to mountaineers, to passes in the mountains and the climbing ways to them, it was not confined to ascents ... This is evidently the origin also of S. rath ... [which] had the same senses as Q., L. ratta, though in mountainous country it was most used of climbing ways ... In Minas Tirith, in the Númenórean Sindarin that was used in Gondor for the nomenclature of places, rath had become virtually equivalent to ‘street’, being applied to nearly all the paved ways within the city. Most of these were on an incline, often steep (NM/364).
Thus Sindarin rath was a blending of √RATH “climb” and ✶ratta “track” < √RAT “find a way”, and in the context of Minas Tirith was generalized to “(city) street” since most of that city’s streets were sloped.
Rath seems to have been used in the sense “climb” or “climbing track” in the name Andrath [= “✱Long Climb”] for the high-climbing pass from Rivendell over the Misty Mountains that Bilbo and the Dwarves took in The Hobbit, as suggested by Christopher Tolkien (UT/271, 278 note #4). However, the name Andrath was also used for the road running from Fornost down to Tharbad (TI/305; UT/348) which was unlikely to climb much, so in that case may have been used in the sense “street”, “track”, or “course”.
Conceptual Development: In The Etymologies of the 1930s, N. rath was also derived from ON. rattha < ᴹ✶rattā̆ under the root ᴹ√RAT “walk”, but in that document it was glossed “course, river-bed” (Ety/RAT). In this sense it was the basis for the river-name N. Rathloriel, translated “Bed of Gold” in narratives from this period (LR/141). This translation of Rathlóriel survived in The Silmarillion as published (S/235), but may have been a remnant of the 1930s meaning of rath.
Neo-Sindarin: Tolkien’s 1968 note implies that original sense of S. rath was a “(climbing) track”, and may have meant “street” only in Númenórean Sindarin, or possibly just for street names in Minas Tirith. For city streets in other contexts I would use [N.] ostrad or [ᴺS.] othrad. I would furthermore ignore the 1930s translation N. rath “course, river-bed”, and would assume that Rathlóriel had a more metaphorical meaning: “✱Golden Street/Track”. For “(river) course” I was instead use the better-attested S. rant; see that entry for details.
Tolkien gave various roots meaning “climb” in the 1940s, 50s and 60s. The first of these was ᴹ√RAP “climb (as a tree by clinging[?])” on a rejected page of verbal roots in the Quenya Verbal System (QVS) from 1948, with a single derived (verb?) form ᴹQ. rampa (PE22/127). In 1957 Notes on Names (NN) Tolkien gave √RET “climb” as part of an explanation of the name S. Orodreth, translated there as “Mountaineer (= ✱mountain climber)”, the only place Tolkien ever explained this name (PE17/182).
The root √RATH “climb” appeared in a 1968-69 explanation of the name S. Amroth as “upclimber, high climber” along with other words like Q. rasillo “squirrel” and Q. rantala “ladder” (UT/245; NM/363, 367). In these same notes Tolkien said S. rath “street” was influenced by this root, as it “applied to all the longer roadways and streets of Minas Tirith, nearly all of which were on an incline” (UT/255 note #16); he also said Sindarin had no other clear derivatives of the root (NM/363). Tolkien briefly mentioned √RAP “climb” in these same notes as a root that Sindarin did have, but this section was rejected (NM/367). Finally √RATH appeared in 1970 green-ink revisions to the Outline of Phonology, but there the root was unglossed (PE19/89 and note #101).
Neo-Eldarin: For purposes of Neo-Eldarin, I think √RAP “climb” is best abandoned, but I think it is worth retaining √RET as well as √RATH (verb vs. noun?), especially since √RATH seems to be unused in Sindarin, with the exception of its influence on S. rath.