The eighteenth line of the Oilima Markirya poem (MC/214). The first word is the adjective lanta “falling” followed by an inflected form ránar of Rána “Moon”. Gilson, Welden, and Hostetter suggest it might be an idiomatic use of the dative (PE16/85), but I think it might be a variant form of the locative: the r-locative.
Decomposition: Broken into its constituent elements, this phrase would be:
> lanta-rána-r = “✱falling-moon-in”
An unglossed adjective, probably meaning “✱fallen”, appearing in The Qenya Phonology of the 1910s based on primitive ᴱ✶lṇ̹ta̜nwa [lṇ́tànwa] (PE12/6).
Neo-Quenya: Both the verb lanta- and the passive/perfective suffix -nwa survive in Tolkien’s later writings, so ᴺQ. lantanwa is still viable as a (Neo) Quenya word.