2. Able to maintain an independent existence or able to live after birth.
3. Capable of success, or continuing effectiveness; practicable; such as, a viable plan or a viable national economy.
Viable was originally restricted to the senses of "able to grow" and "able to survive"; as, in a viable fetus.
Its extended sense of "able to be done" or "worth doing"; as, in "viable alternatives", is now well established and acceptable in the English language.