n The core, center, or essence of an object or system.
n (botany) The central (usually edible) part of a nut, especially once the hard shell has been removed.
n (botany) A single seed or grain, especially of corn or wheat.
n (botany, US) The stone of certain fruits, such as peaches or plums.
n A small mass around which other matter is concreted; a nucleus; a concretion or hard lump in the flesh.
n (computing) The central part of many computer operating systems which manages the system's resources and the communication between hardware and software components.
n (computing) The core engine of any complex software system.
n (programming) The simplified input to an algorithm that has undergone kernelization.
n (calculus) A function used to define an integral transform.
n (mathematics) A set of pairs of a mapping's domain which are mapped to the same value.
n (mathematics, linear algebra, group theory, functional analysis) For a given function (especially a linear transformation between vector spaces or homomorphism between groups), the set of elements in the domain which are mapped to zero; (formally) given f : X → Y, the set {x ∈ X : f(x) = 0}.
n (mathematics, category theory) For a category with zero morphisms: the equalizer of a given morphism and the zero morphism which is parallel to that given morphism.
n (mathematics, fuzzy set theory) The set of members of a fuzzy set that are fully included (i.e., whose grade of membership is 1).
n (slang) The human clitoris.
n (chemistry) The nucleus and electrons of an atom excluding its valence electrons.
v To enclose within a kernel
v To crenellate