A verb appearing in the Gnomish Lexicon of the 1910s as G. paptha- “tremble, quiver” (GL/63), clearly derived from the early root ᴱ√PAPA that was the basis for ᴱQ. papa- “tremble” (QL/72).

Neo-Sindarin: Since I retain ᴺ√PAP “tremble” as a Neo-Root, I would adapt this verb for purposes of Neo-Sindarin as ᴺS. potha- “to tremble, quiver”, with the Sindarin sound changes whereby apth vocalized to auth and then au became o as was usual in polysyllables.