A noun appearing as G. tîl “cicatrice, scab, healing of a wound” in the Gnomish Lexicon of the 1910s derived from the early root ᴱ√TELE “cover in” (GL/70), hence probably referring to the scab as the covering of a wound. Likely the primitive form was *tēl- since ancient ē became ī in Gnomish.

Neo-Sindarin: The root √TEL-U was still associated with roofs and coverings in Tolkien’s later writings, and the sound change ē > ī also remained a feature of Sindarin, so I’d retain this word as ᴺS. tîl “scab, cicatrice, healing of a wound” for purposes of Neo-Sindarin, perhaps from primitive *tēlŭ.