How to translate impossible
Choose the way of translating this concept based on the meaning you're trying to get across.
ori umaan: very difficult
ori urakto: very difficult.
(Some people specify a difference in the two terms, with umaan as "grueling" and urakto as "challenging.")
nu lise banar: can't happen; not be able to happen
nu lise vaabir: can't do; not be able to do
ne'cuyla: improbable, not likely
Research notes: We can't start with retyc because it's related to ret ("maybe"), and "impossible" means "to not be able to" rather than "not with uncertainty" (which is what ne'retyc means).