Sentence:  As we have stated before, a curve f' is <WSD>adjoint</WSD> to a curve f if it have at least the multiplicity r_i-1 at each point where f has the multiplicity r_i. A first polar \sum_i y_i \left ( \partial f / \partial x_i \right ) = 0 is an example of an <WSD>adjoint</WSD> curve. 
Meaning of the word marked with <WSD> tags:  Having a relationship of the nature of an '''adjoint''' (adjoint curve); sharing multiple points with.