The unglossed root ᴱ√SIRIP is one of the few triconsonantal roots appearing in the Qenya Lexicon of the 1910s, where it had derivatives ᴱQ. siripta “slender stem” and ᴱQ. sirpe “stem, stalk, slender tube, etc.” (QL/84). In the contemporaneous Gnomish Lexicon it had derivatives like G. sirp “straw” (GL/68) but also G. thribin “lean” and G. thrimp “stalk” from *s(i)rip- (GL/73) since initial sr- became thr- in Gnomish.

Neo-Eldarin: I think it is worth positing a Neo-Root ᴺ√THIRIP “stalk” to salvage some of these early words. I prefer ᴺ√THIRIP over just keeping ᴱ√SIRIP unchanged because (a) it better preserves the forms of more Gnomish words and (b) helps differentiate the Neo-Root from 1930s ᴹ√SRIP “scratch” (Ety/SRIP).