Sentence:  An algebraic extension L/K is called "simple" if L=K(\alpha) for some \alpha\in L. The element \alpha is called a <WSD>"primitive element</WSD>" for L/K. Every finite separable algebraic field extension is simple. / Suppose that L = K(\alpha_1,·s\alpha_r) is a finite separable extension and K_0\subseteq K is an infinite subset of K. Then there exists a <WSD>primitive element</WSD> \alpha of the form \textstyle\alpha = \sum_{i=1}^r c_i\alpha_i with c_i\in K_0. 
Meaning of the word marked with <WSD> tags:  An element that generates a simple extension.