ᴱ√SUKU¹ root. “*resin, gum”
ᴱ√SUKU⁽¹⁾ appeared as an unglossed root in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. súke “resinous tree, pine or fir” and ᴱQ. sulka “sticky, viscous” (QL/86-87). It had derivatives in the contemporaneous Gnomish Lexicon such as G. thuctha- “adhere to, cleave” and G. thugli “resin” (GL/73), indicating the true root form was *ᴱ√ÞUKU. I think it is worth positing a Neo-Root ᴺ√THUK “resin, gum” to salvage some of these early words.
Reference ✧ QL/86 ✧ SUKU