One of various roots for “small” Tolkien used in his later writings. The root √NIK “small” first appeared in notes on Eldarin Hands, Fingers and Numerals from the late 1960s (VT47/26; VT48/18), but was connected to the diminutive suffix ✶-i(n)ki which had a much longer conceptual history. One of the earliest known diminutive suffix was ᴱQ. -íne(a) in the Qenya Lexicon of the 1910s from the root ᴱ√INI “small” (QL/42), which might be a precursor to √NIK; these suffixes reappeared in the Early Qenya Grammar of the 1920s (PE14/49, 81). In the Gnomish Grammar of the 1910s, the word G. inc “small” was used as the basis for the “diminutive superlative” -inci (PE11/16).
In the Qenya Lexicon, Tolkien connected ᴱ√INI “small” to the root ᴱ√MINI of similar meaning (QL/42, 61). There are no signs of ᴱ√MINI “small” in the contemporaneous Gnomish Lexicon, but the word G. migin “little” (GL/57) hints at a (hypothetical) variant root ✱ᴱ√MIKI. Further support for ✱ᴱ√MIKI can be found in other diminutive forms in the Early Qenya Grammar of the 1920s such as prefixal diminutive ᴱQ. mike- along adverbial ᴱQ. mike “little” (QL/48, 81), the latter appearing with the gloss “a bit” in the English-Qenya Dictionary from this period (PE15/70) along with other similar words in both the dictionary and the grammar. This ✱ᴱ√MIKI might be another precursor to √NIK. An early hint at √NIK itself might appear in the word ᴹQ. nikse “minnow, little fish” from the Declension of Nouns from the early 1930s (PE21/27).
In Noldorin and Sindarin, the primary diminutive suffix became -eg, which was connected to the Common Eldarin suffix -iki elsewhere in notes on hands and fingers (VT47/14 note #21). In the notes where √NIK “small” appeared in the late 1960s, Tolkien gave the primitive diminutive as -inkĭ along with variants ikki, -iksi, -si, -ensi, -ki.
One of the main competing roots for “small” was ᴹ√PIK [see the entry for √PI(N)], itself with a lengthy conceptual history. The shift of pitya >> nitya “little” in the father name of Amrod from the late 1960s may represent a replacement of √PIK by √NIK (PM/365), but I think it is likelier the two roots coexisted with slightly different meanings, as was the case for their earlier precursors. In the notes from the late 1960s, √NIK was also contrasted with √NIP “small (usually with connotation of weakness)” (VT48/18), from which the word S. niben “petty” was derived, as in S. Nogoth Niben (WJ/388).
Neo-Eldarin: For purposes of Neo-Eldarin, I would assume √NIK meant “small” in a neutral sense, √PIK “tiny” (along with variants √PĪ and √PIN) and √NIP “small and weak”. I would use these as the major Eldarin roots for “small” words, along with a number of other more specialized roots.
This root appeared as ᴹ√NIM “it appears, occurs to (one’s mind)” in the first version of notes on Quenya Personal Pronouns (QPP1) from the late 1940s, with modern Quenya nimin(ye) “it seems to me” (PE23/89). In Quendian & Common Eldarin Verbal Structure (EVS1) from this same period, Tolkien had nemini “appears/seems to me”, revised to nimini, which was deleted and a new paragraph was written with nemin “it seems to me” (PE22/93 note #6 and #7).
In the Quenya Verbal System from 1948 Tolkien used nem- (PE22/99-100, 105, 111), and in Common Eldarin: Verb Structure (EVS2) from the early 1950s had Q. {nemeste} nemesta “appearance, seeming” (PE22/137). Eldarin Pronouns (EP1) also from the early 1950s had the root √NEM as the basis for ✶nemi-ne “it appears to me, me seems” (PE23/123). The forms Q. níma/nimulë and S. nîf/nivol appeared in 1957 notes, all glossed “phantom” or “seeming”, indicate Tolkien may have restored ✱√NIM “seem”. I prefer to stick with better attested √NEM for purposes of Neo-Eldarin.