in medicine, is when a humour which cannot conveniently be evacuated at the part affected, is attracted from thence, and discharged elsewhere; thus, a blister is applied to the neck to draw away the humour from the eyes.

The doctrine of derivation and revulsion so much talked of by the ancients is, in their sense of these terms, wholly exploded. By revulsion, they meant the driving back of the fluids from one part to another. The only rational meaning the word revulsion, as here applied, can have, is, the preventing too great an afflux of humours to any part, either by contracting the area of the vessels, or diminishing the quantity of what flows from them; the first of these intentions is answered by the application of repellents to the part; the last by bleeding, and other evacuations; thus, any medicines promoting the secretions, may be said to make a revulsion; and in this sense derivation can only be understood.

grammar, the affinity one word has with another, by having been originally formed from it. See Derivative.