√IS root. “know”
The root √IS was the basis for words having to do with “knowledge” for all of Tolkien’s life, as represented by the verb Q. ista- “to know” which likewise retained the same form and meaning for decades. The root first appeared as ᴱ√ISI¹ in the Qenya Lexicon of the 1910s, where somewhat cryptically Tolkien said its Gnomish form was GIS or IS (QL/43). This is mysterious because there were no such Gnomish words beginning with gis- in the contemporaneous Gnomish Lexicon, but there is an Early Noldorin word ᴱN. gist- “to know” from the 1920s, probably derived from ᴱ✶ʒist- (PE13/144, 146); in this early period initial ʒ- > g- in Gnomish (PE12/17).
Tolkien seems to have abandoned this Noldorin variant, giving the root only as ᴹ√IS in The Etymologies of the 1930s (Ety/IS). In this form it continued to appear in Tolkien’s later writings (PE17/155; PE22/129; VT41/6; VT48/25). In one place Tolkien gave the root in inverted form √SI (PE22/134), and such an inversion appeared in some of its derivatives, such as Q. síma “imagination, mind” (VT49/16) and sinte the irregular past tense of Q. ista-. However, the vast majority of its derivatives are from √IS.
References ✧ PE17/155; PE22/129, 134; VT41/6; VT48/25
ᴹ√IS root. “*know”
References ✧ Ety/IS, PHIN
ᴱ√ISI¹ root. “*know”
References ✧ LT2A/Eldarissa; QL/43