Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!

Qenya 

sanar(yas)

adverb. *on that day (mentioned)

The correlatives ᴹQ. sanar and sanaryas appeared in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/109), a combination of ᴹQ. sa “that (mentioned)” and ᴹQ. -ar(yas) “day”.

Neo-Quenya: For purposes of Neo-Quenya I would update this to ᴺQ. sanaurë “on that day (mentioned)” using Q. aurë for “day”.