如：基本理論,基本方法.
primary基本的;本來的；初級的,初等的;基層的
The primary meaning of the word isn't used now,but you can look it up in a big dictionary.
這個字的本義現在不用了,但妳可以在大字典裏查到.
I started primary school when I was 5 years old.
我五歲時開始讀小學.
essential本質的,實質的;基本的；必要的,不可缺的
它和上面的兩個意思相差比較大
There is no essential difference between the two drafts.
兩份草稿沒有本質上的不同.