A noun described as a “circular mound or artificial hill” in the Unfinished Index of The Lord of the Rings, appearing in the place name Cerin Amroth “Amroth’s Mound” (RC/309; LotR/350).
Conceptual Development: In The Etymologies of the 1930s, N. cerin was glossed “round enclosure” as a derivative of the root ᴹ√KOR “round” (Ety/KOR; EtyAC/KOR). This in turn was a later iteration of ᴱN. gwerin “enclosure” from Early Noldorin Word-lists of the 1920s (PE13/146), which was itself a later version of G. gorin or gwarin “circle of trees” in the Gnomish Lexicon of the 1910s (GL/47), first given as corin “an enclosure, especially a (sacred) circular enclosure fenced with trees” (GL/26), but the meaning of that last word was changed to adjectival “round, circular; rolling”. Note that corin “enclosure” also reappeared in the Early Noldorin Grammar of the 1920s, only to be deleted again (PE13/121).
Thus it seems 1910s {corin >>} gorin “enclosure or circle of trees” >> 1920s {corin >>} gwerin “enclosure” >> 1930s cerin “round enclosure”. As for Cerin Amroth, Tolkien described it as follows: “Upon it, as a double crown, grew two circles of trees: the outer had bark of snowy white, and were leafless but beautiful in their shapely nakedness; the inner were mallorn-trees of great height, still arrayed in pale gold. High amid the branches of a towering tree that stood in the centre of all there gleamed a white flet (LotR/350).” Thus, perhaps this name originally referred to the rings of trees, and only later did Tolkien decide that cerin referred to the mound itself.
Neo-Sindarin: For purposes of Neo-Sindarin, I would use this word mainly in its 1930s meaning “round enclosure”, but would assume it could also be used of round things in generally, such as a mound, that surrounded something in the middle, such as the great tree at the center of Cerin Amroth.
n.