Q. ciuca n. “*thigh” (Category: Leg)
Tolkien used a number of different “thigh” words in Quenya throughout his life. The earliest of these was ᴱQ. tyū “thigh” in the Qenya Lexicon and Poetic and Mythological Words of Eldarissa based on the early root ᴱ√TYU, a variant of ᴱ√TIW̯I “thick” (QL/50, 93; PME/93). In Early Noldorin Word-lists of the 1920s, this became ᴱQ. tyúta from primitive ᴱ✶teutá (PE13/154), which became ᴹQ. tyúka in the Declension of Nouns from the early 1930s (PE21/8), and finally ᴹQ. tiuko “thigh” in The Etymologies written around 1937 from primitive ᴹ✶tiukō under the root ᴹ√TIW “fat, thick” (Ety/TIW).
In the Outline of Phonetic Development (OP1) also written the late 1930s, Tolkien instead had ᴹQ. kiuka “thigh” from the root ᴹ√KIWIK (PE19/54). This form and root reappeared as Q. kiuka in the Outline of Phonology (OP2) from the 1950s, though Tolkien clarified the pronunciation was actually kyūka in Tarquesta since iu became a rising diphthong [ı̯ū] (PE19/107).
Neo-Quenya: For purposes of Neo-Quenya, I would stick with the derivatives of the 1937 root ᴹ√TIW “fat, thick” since this represents a larger collection of words, and so would use [ᴹQ.] tiuco for “thigh”, pronounced tyūko.
References ✧ PE19/107
|✶kiukā > kiuka||[kiukā] > [kiuka]||✧ PE19/107|
ᴹQ. kiuka n. “thigh” (Category: Leg)
Reference ✧ PE19/54 ✧ ciuca “thigh”
|ᴹ✶kiukā > ciuca||[kiukā] > [kiuka]||✧ PE19/54|
ᴹQ. tiuko n. “thigh” (Category: Leg)
Reference ✧ Ety/TIW ✧ “thigh”
|ᴹ✶tiu̯kō > tiuko||[tiukō] > [tiuko]||✧ Ety/TIW|
ᴹQ. tyúka n. “thigh” (Category: Leg)
References ✧ PE21/8
|tyúkasta||genitive dual||“of two thighs”||✧ PE21/8|
ᴱQ. tyú(ta) n. “thigh” (Category: Leg)
References ✧ PE13/154; PME/50, 93; QL/50, 93
|ᴱ✶teutá > tyúta||[teutā] ? [tʲūta]||✧ PE13/154|
|ᴱ√TYU > Tyû||[tʲū]||✧ QL/50|