Longman Dictionary of Contemporary English - essential

~1 adj 1 extremely important and necessary in order to do something correctly or successfully  (If you're going walking in the mountains, strong boots are essential.) + for/to  (Good food and plenty of exercise are essential for a healthy life. | it is essential (that))  (It is essential that the oil is checked every 10,000km. | it is essential to do sth)  (It's essential to read the small print at the bottom of any document.) 2 the essential parts, qualities, or features of something are the most important, typical, or noticeable ones  (The essential character of the village has not changed in over 300 years. | essential difference/feature/point etc)  (The essential difference between man and apes is intelligence.) ~2 n 1 C usually plural something that is important because it is necessary for life or for doing something  (The charity provides homeless people with essentials like food and clothing. | bare essentials (=the most necessary things))  (We don't have much room for luggage so we're only taking the bare essentials.) 2 the essentials the basic and most important information or facts about a particular subject  (the essentials of English grammar)