essentialsn.要件；概要essentialadj.本质的；必要的；重要的n.要素；必需品essential assumption基本假设essential difference主要区别essentially negative基本阴性essential activation基本激活作用essential congruence本质同余essential courseware精品课程essential properties基本性能, 基本性质, 必然属性Essential principles基本原则essential attributes本质属性essential definition实质定义