essential/ɪˈsenʃ(ə)l/
adj.1. 必需的；基本的Food is essential to life.食物是维持生命不可或缺的。
Her most essential quality is kindness.她最主要的品质是厚道。
It is essential for us to try to decide whether television is a blessing or a curse.我们有必要来评断电视到底是福还是祸。
What is the essential difference between these two economic systems?这两种经济体制的本质区别是什么？
2. 提炼的；精华的essential oils香精油