Sonja hasn't published her book, the official wiki isn't all filled in either.
The 117~120 word list can still be found in the wayback machine and place like this:http://en.wikibooks.org/wiki/Toki_Pona/WordTpEn
where indeed, it is marked as (n.)
It's been an open question if words can be used outside of the official part of speech. I've seen people post the opinion that the phrase "part of speech" doesn't apply to toki pona as well as it does in natural languages, so marking linja
as noun isn't all that meaningful.
The alternate theory is that one should only put "linja
" in head noun positions, after pi, after preps, etc.. I don't see too many people strictly following this, and less often do you see anyone being corrected for using a word outside of the official part of speech.
Here is a few community innovation examples from the wikia (not necessarily canon) using linja in a modifier position:http://tokipona.wikia.com/wiki/telo_linja
and from a fan page...http://anadder.com/toki_pona/song_of_songs
"...anpa sinpin li sama e tomo linja pi kiwen walo...." chin is like house-linear of white rocks" chin like marble columns.