[caista] ("k"), fraction "one tenth" (1/10), also cast, an unusual Quenya form since the language does not normally tolerate two consonants finally (VT48:11). Compound caistanótië ("k") "decimal system" (in counting) (ibid.) However, Tolkien later rejected the root KAYAN "ten" in favour of KWAYA(M), changing the cardinal "ten" from cainen to quain, quëan (VT48:13). Apparently we must therefore read *quaista as the new fraction "one tenth".
Quenya
caista
fraction. one tenth
caista
one tenth
quaista
one tenth
*quaista, reconstructed/updated fraction "one tenth"; see caista.
quaista
fraction. one tenth
cast
one tenth
[cast] ("k"), fraction "one tenth", but the form is apparently obsolete; see caista. (VT48:11)
cast
fraction. one tenth
A word appearing as kaista or kast “1/10” in notes on numbers from the late 1960s, a combination of √KAYAN “ten” with the fractional suffix -sta.
Neo-Quenya: Since I prefer quëan for “ten”, I would use ᴺQ. quaista “one tenth” for purposes of Neo-Quenya as suggested by Helge Fauskanger (QQ/quaista).
Conceptual Development: The Early Qenya Grammar of the 1920s had ᴱQ. keatto or kesto “one tenth” with adjective forms ᴱQ. keatya or kestya (PE14/51, 84). All of these words were related to 1920s ᴱQ. kea “ten”.