A word for “crest, ridge” (PE17/24) or a “long (low) hill with a sharp ridge against the skyline” (PE17/97). Tolkien seems to have coined this word to explain the abnormal “double plural” form pinnath in S. Pinnath Gelin “Green Hills or Ridges” (LotR/771; RC/525). It is clear he originally intended pinnath to be derived from S. pend “slope” < √PED, but it was a somewhat peculiar combination of the normal plural form pind with the class plural suffix -ath (PE17/24). By introducing S. pind “ridge” < √KWIN, Tolkien resolved this quandary (PE17/158).
Conceptual Development: The notion of this “double plural” form dates all the way back to the Early Noldorin Word-lists of the 1920s, where it seems the noun ᴱN. binn “slope, hillside, bank” was developed from the plural form of the adjective ᴱN. benn “sloping”, and the plural of the noun was binniath (PE13/138, 160). It seems likely that pinnath was initially a remnant of this double pluralization, before Tolkien reconceived of it as a derivative of √KWIN.
A root Tolkien introduced to explain S. pinnath “ridges” (class plural of pind) in Pinnath Gelin “Green Ridges” (PE17/173). It appeared below √PED “fall in steep slant, incline, slope”, which was the basis for the similarly formed S. pend “slope”. In notes elsewhere Tolkien said that pinnath was a blending of the two plural forms of pend: general plural pind and class plural pennath (PE17/24), but it seem he later decided pind was from the distinct root √KWIN.