The one-word substitute for something that is capable of being accomplished is "Feasible."

• Feasible: Feasible means capable of being done, achieved, or implemented. It implies that something is practical, possible, and achievable.
• Untenable: Untenable means not capable of being defended, supported, or sustained. It refers to something that is unreasonable or unsustainable.
• Irrevocable: Irrevocable means not capable of being changed, reversed, or undone. It pertains to something that is final and cannot be altered.
• Eligible: Eligible means qualified or entitled to participate or be considered for something. It does not convey the sense of being capable of being accomplished, but rather being suitable or meeting certain criteria.