ᴺS. !pess² n. “feather” (Category: Feather)
G. pectha n. “plume” (Category: Feather)
The word G. pectha “plume” appeared in the Gnomish Lexicon of the 1910s, along with G. pecthon “plume, feather” (GL/63-64), clearly cognates of ᴱQ. pekte “plume” under the early root ᴱ√PEKE (QL/73).
Neo-Sindarin: Somewhat surprisingly, there are no later “plume” or “feather” words in the currently published materials from Tolkien’s writings on Noldorin and Sindarin of the 1920s or later. Most Neo-Sindarin writers use ᴺS. pess for “feather” as the analog of word Q. quessë, which Tolkien used in the 1930s-1960s. Hialmr added this Neo-Sindarin word to the VinQuettaParma Wiki (VQP) in 2015, but it has likely been floating around for much longer. As for “plume”, I personally would use an augmentative form: ᴺS. pesson “plume, (great) feather”.
Reference ✧ GL/63 ✧ “plume”