essential adj.
VERBS appear, be, seem | become It is becoming almost essential for students to have a second language. | remain | make sth Increased competition makes it essential for the business to innovate. | consider sth, deem sth, regard sth as, see sth as, think sth Do you consider these textbooks essential for the course?
ADV. really | absolutely | almost, virtually | fairly | by no means Although useful, the accessories are by no means essential.
PREP. for the skills essential for success | to He believed that some form of religion was essential to human life.
You can also check other dicts: essential (English, 中文解释 ), wordnet sense, Collins Definition