Step 1: Meaning of the word "assent."
"Assent" refers to the expression of agreement or approval.
Step 2: Analysis of the options.
Distance refers to the space between two points, unrelated to the meaning of "assent."
Accent refers to a distinctive way of pronouncing words, unrelated to the meaning of "assent."
Consent refers to giving permission, which is a synonym of "assent," not an antonym.
Dissent refers to disagreement or the expression of disapproval, which is the opposite of "assent."
Step 3: Conclusion.
Thus, the correct antonym of "assent" is dissent.
Final Answer:
\[
\boxed{\text{Dissent is the correct antonym.}}
\]