Noun > Core
1 : the central part of a fruit (such as an apple) that contains the seeds
an apple core
2 : the central part of something
the core of a golf ball
The pads have a foam core.
the engine core
3 : the most important or basic part of something
Lack of money is the core of the problem.
The core of the government’s plan is to provide loans for small businesses.
voters who form the core of the party
The economy is at the very core of this year’s election.
4 : technical: a part that has been removed from a material for scientific study
took a core sample of rock
an ice core from the glacier
5 : technical: the place in a nuclear reactor where the reaction takes place
the reactor core
to the core
in a very complete or extreme way — used for emphasis
He is patriotic to the core. (=he is extremely patriotic)
Her family is English to the core.
He’s rotten to the core. (=he’s a very bad/dishonest person)
They were shaken to the core. (=extremely shaken/upset)