WordNet sense 1 (capable of being imagined):

imaginable

WordNet sense 2 (capable of being done with means at hand and circumstances as they are):

feasible, practicable, viable, workable

WordNet sense 3 (within the bounds of what may be conceived within the framework of nature):

conceivable

WordNet sense 4 (capable of existing or taking place or proving true; possible to do):

doable

WordNet sense 5 (potentially existing but not presently evident or realized):

latent

WordNet sense 6 (existing in possibility):

potential