arn (prefix “royal”) + gond (“great stone, rock”) + ath (collective plural suffix). Triconsonantal cluster rgn produces rg; in this case original nd doesn’t produce nn before the collective plural suffix ath. #It might be a dialectal form or a mistake on the part of Gondorians who didn't always use Elvish languages correctly (VT42 “Rivers and Beacon-hills”).
Sindarin
argonath
place name. Pillars of the Kings, (lit.) Royal Stones
Argonath
noun. royal stones
Argonath
Argonath
The name is Sindarin and is composed of ar "royal" plus gond "stone". The ending -ath is a collective plural, used sometimes (perhaps irregularly) for dual.
Argonath
Argonath (name)
gondrath
street of stone
(i ’ondrath) (causeway, raised stone highway), pl. gendraith (i ngendraith = i ñendraith). Archaic pl. göndreith. (WJ:340)
sarn
stone
1) (small stone, or stone as material) sarn (i harn, o sarn), pl. sern (i sern); also used as adj. ”stony, made of stone”. 2) gôn (i **ôn, construct gon); pl. gŷn, coll. pl. #**gonath as in Argonath. 3) (larger stone) gond (i **ond, construct gon) (great stone or rock), pl. gynd (i ngynd = i ñynd), coll. pl. gonnath** (Letters:410).
gôn
stone
(i ’ôn, construct gon); pl. gŷn, coll. pl. #gonath as in Argonath.
gond
noun. great stone, rock
gond
stone
_n. _stone, rock. Archaic S. gond > gonn. Q. ondo. >> Gondor
gondren
adjective. (made) of stone
sarn
noun. stone (as a material)
Sern in UT/463 is a misprint, see VT/42:11
sarn
noun. small stone
Sern in UT/463 is a misprint, see VT/42:11
gond
stone
(i ’ond, construct gon) (great stone or rock), pl. gynd (i ngynd = i ñynd), coll. pl. gonnath (Letters:410).
gondren
made of stone, stony
(stony), lenited ’ondren, pl. gendrin. Archaic pl. göndrin (TI:270).
gonhir
master of stone
(i ’Onhir), no distinct pl. form except with article (i Ngonhir = i Ñonhir), maybe primarily used as a coll. pl. Gonhirrim (WJ:205, there spelt ”Gonnhirrim”)
sarn
stone
(i harn, o sarn), pl. sern (i sern); also used as adj. ”stony, made of stone”.
sarn
made of stone, stony
(lenited harn; pl. sern); also used as noun ”small stone, pebble, stone [as material]”; as adj. also = ”stony”.
Two statues of Gondorian kings just north of Nen Hithoel, translated “Pillars of the Kings” (LotR/392), more literally “(Pair of) Royal Stones” (RC/347, RGEO/67, Let/427). It is combination of the prefix ar(a)- “noble”, the noun gond “stone”, and the class-plural suffix -ath (RC/347).
It is not clear why this noun uses the class-plural. However, in one place Tolkien describes a dual variant argonad using the archaic dual suffix †-ad (Let/427). Perhaps this was the original form of the name, altered to Argonath after the Sindarin dual form was forgotten.
Conceptual Development: In Lord of the Rings drafts from the 1940s, this name first appeared as N. Sern Aran(ath) “King Stones” along with an alternate name N. Sern Ubed “[Stones of] Denial” (WR/98, 132). Later in these drafts it was revised to N. Argonath (TI/366).