A word for “then” appearing in a list of demonstratives from 1968, a vowel-lengthened form of ta “that” (VT49/11). It reappeared in some notes from 1969 alongside a variant tai (VT49/33). ᴹQ. tá “then, at that time (past now)” appeared in Demonstrative, Relative, and Correlative Stems (DRC) from 1948, where Tolkien indicated it was specifically used to refer to the past (PE23/109), as opposed to ᴹQ. en “then” referring to the future.
Primitive elvish
tha
pronoun. tha
thā
adverb. then, next
aw’tha
noun. a dim shape, spectral or vague apparition
kha
pronoun. kha
ta (4) conj., said to be a reducted form of tá "then", used "before each new item in a series or list"; "if as often in English the equivalent of and was omitted, and placed only before a final item [e.g. Tom, Dick, and Harriet], this would in Quenya represent a discontinuity, and what followed after ta would be an addition of something overlooked or less important". (PE17:70) Hence the use of arta (ar ta, "and ta") for "et cetera"; in older language ta ta or just ta.