So far we've been making words like "killable", "destructible", or "doable" fairly literally with our invented word "Tok" for able".  This idea uses the canon "Vis", "can", as an alternative prefix to make these instead.  "Killable" would be "Viskrii", "can-kill", "destructible" would be "Visald", "can-destroy", and "doable" would be "Visdreh".

Then, words like "unkillable" or "indestructible" would use "Nis", "cannot", instead of the usual "Vo-". "Unkillable" would be "Niskrii", "indestructible" would be "Nisald", "undoable" would be "Nisdreh".

My reasoning for this idea is that it would root more of our words in canon, and it would help to simplify them as well. Thoughts?

It seems to me like the "tok" suffix should make, say, "kriitok" mean "able to kill", as opposed to "able to be killed", because of the literal meaning of the English word "able". However, to use "vis" also seems to me like it should make the word "viskrii" mean "can kill", as opposed to "can be killed".

The use of "tok" for the equivalent of the English "-able" seems to me like it's taking Dovahzul another step closer to English, which is some sort of trend that I'm seeing, and I don't want that (I think it's a very American thing to do). So it seems to me like a change in this would help, but I'm not sure what's best.

As a prefix, we could say that "Vis" implies "can be ____", so that "Viskrii" would make "can be killed" rather than "can kill". Alternatively to avoid confusion, would could make new prefixes like "Vi-" and "Ni-" to mean "can be ____" and "cannot be ____" just so people don't try and puzzle out "Vis" and "Nis" too literally.

The "vi-" and "ni-" prefixes seem like a better idea to me.

"Tok" is completely original, so my opinion is already biased towards using compounds made of the canon word "Nis" and semi-canon "Vis."

It seems to me like the "tok" suffix should make, say, "kriitok" mean "able to kill", as opposed to "able to be killed", because of the literal meaning of the English word "able". However, to use "vis" also seems to me like it should make the word "viskrii" mean "can kill", as opposed to "can be killed".

"Able" and the suffix "-able" have only the root meaning in common, but little else. "X + -able" will almost always mean "possible of having X done to (whatever is described with the adjective)" - "killable" is always "can be killed" and never "can kill". In English, there is no chance of such a suffix making the meaning ambiguous.

The real question is, as Hiith has correctly pointed out, do we let this affect Dovahzul? The suffix "-able" does come from the "able," so considering Dovahzul is an ancient - and by any normal accounts a more-or-less-dead  language - and had therefore undergone little change from its primeval form, we could argue on the side that combinations such as "Viskrii" could possibly mean both "killable" and "able to kill."

Personally, I am inclined to oppose that option, simply because of the possibility of two completely opposite translations of the same word, as well as the fact that we don't really need a word to say "able to kill" - we can just call that person "Kriid" or "killer;" what is a killer but one who has shown their capability to kill?

All in all, I fully support the variants of "Vis-" and "Nis-" for the meanings of "X-able" and "un-X-able".