► possibleable to be done: Travel to another planet may soon be possible. There are two possible ways to solve the problem.
► feasible possible and able to be done in a practical way: It is not feasible to rewrite the entire program.
► realistic possible and based on what someone can really achieve: Do you think the team has a realistic chance of winning?
► viable possible and likely to be successful: Will solar power ever be a viable alternative to oil?
► workable possible and likely to be usable or effective without too much trouble: I hope we can find a workable solution to the problem.