The innermost or central part of a thing; the essential or vital part; the spirit or essence; the core, the nub. Frequently in pith and marrow.

The essential part of something; the sum and substance of; the greater part or number. Obsolete (Scottish in later use).

The vital, principal, or most necessary part of something. Obsolete.

figurative. The core or central part of anything non-material; the gist of a narrative, the basis of a system, etc.

The essential part of something. Obsolete.

In figurative contexts: a person or thing occupying a high, central, or vital position in something likened to an arch or similar structure.

transferred. Parts or features essentially necessary to something; essential points, essentials.

A narrow part, place, or thing; the narrow part of something. gen. Obsolete.

(Const. of.) That which accounts for something surprising or extraordinary; the essential thing to be observed in order to secure some end.

figurative. A centre of power, activity, or interest. Cf. nerve centre n. (b) at nerve, n. compounds 2.

The heart of a matter; the crux or central point of a discussion, argument, etc.

As a count noun: a primal thing; an essential or fundamental concept. As a mass noun: the quality or condition of being primal; primacy.

A word or idea that serves as a solution or explanation for something; a word, expression, or concept of particular importance or significance.

The heart of a matter; the crux or central point of a discussion, argument, etc.; = nub, n.1 3.

a keyword; a catchword or expression currently fashionable; a term used more to impress than to inform, esp. a technical or jargon term.

a fashionable word, a buzz word.