crux
n. countable C1 Advanced US //ˈkɹəks// UK //kɹˈʌks// crux
n. the most important part of a problem or an argument. It is the central point that everything else depends on.
n. the most essential or decisive point of an issue or argument. Often used to identify the core element that must be resolved to reach a conclusion.
The crux of the matter is that we lack funding.
After hours of debate, the committee finally reached the crux of the problem: the software was simply incompatible with the old hardware.
While the lawyers argued over minor procedural details, the judge reminded them that the crux of the case remained whether the defendant had acted with clear intent.
Learned borrowing from Latin crux (“a cross”).
Usage
Usually appears in the singular form, often in the phrase 'the crux of the matter'.