An adverb for “athwart”, also used for “(to a point) beyond” in notes from 1965 (PE17/65). It appears to be an allative form of √LAŊ “beyond”.
Neo-Quenya: For purposes of Neo-Quenya, I would also use lanna to mean “across”.
Conceptual Development: The Gnomish Lexicon of the 1910s mention ᴱQ. arta as equivalent to G. adr(a) “athwart” (GL/17), clearly based on the early root ᴱ√TARA (QL/89).
lanna prep. "athwart" (PE17:65)