Each of these words has certain meanings that they do not share, but in the sense of stating that something is not true, repudiate is the stronger, more emphatic term. One might deny that water seeks its own level; he might repudiate all of mankind's accumulated observation and experience. Similarly, a father might deny a daughter use of the family automobile, but he would repudiate her only if he disowned her or threw her out of the house. See also refute.
Dictionary of problem words and expressions. Harry Shaw. 1975.