ESSENTIAL
ADJECTIVES
1607 — PEREMPTORY absolutely essential; important, vital
1615 — SINE QUA NON indispensable, absolutely necessary or essential
1622 — EXTRINSIC not essential or inherent
1964 — GUT basic; essential; most immediate → Amer. sl.
1990 — MUST-HAVE essential, mandatory; usually used in the context of material objects → sl.
ADVERBS
1604 — PRIMORDIALLY basically, fundamentally; essentially
NOUNS
1595 — THE MAIN OF ALL the important or essential point → obs.
1632 — IMPLEMENT something necessary to make a thing complete; an essential or important constituent part → obs.
1635 — PITH AND MARROW the essential or important part
1663 — GUTS the essentials; the most important part; the inner and real meaning; the essence of a matter → UK
1820 — TONGUE OF THE TRUMP n. the most important person or thing; the principal person in any undertaking; the leader; that which is essential to the success of anything → Sc.
1839 — MUST-HAVE something which is regarded as being essential or highly desirable to have
1863 — MARROW the centre, the essential part, the best of anything; the main point, or the full meaning → Ireland & Eng. dial.
1899 — QUINTESSENTIAL n. the most essential part of a thing
1942 — NITTY-GRITTY the fundamentals, the essentials, the basics → orig. African-American
1987 — NITTY the fundamentals, the essentials → US sl.
VERBS
1935 — THROW AWAY THE BABY WITH THE BATHWATER to reject what is essential or valuable along with the inessential or useless
Lexicophilia 