The word "ignoble" refers to something dishonourable, base, or not deserving of respect. 

A. criminal: This word is not the opposite of "ignoble." Some criminal acts are actually considered ignoble.

B. ignorant: "Ignorant" refers to a lack of knowledge or awareness, which is not the opposite of dishonourable behaviour. Option B is not the best opposite in this context.

C. honourable: This word is the most suitable opposite for "ignoble." "Honourable" refers to actions or behaviour that is characterized by integrity, fairness, and moral uprightness.

D. selfish: "Selfish" refers to prioritizing one's own interests over others, and it doesn't directly oppose the idea of dishonourable behaviour. Option D is not the best opposite.

Therefore, option C, "honourable," is the most appropriate choice as it directly contrasts with the dishonourable nature implied by "ignoble."