crux 
(krŭks, krks)
(krŭks, krks)n. pl. crux·es or cru·ces (krsēz)
1. The basic, central, or critical point or feature: the crux of the matter; the crux of an argument.
2. A puzzling or apparently insoluble problem.
3. The most difficult portion of an ascent in rock climbing or mountaineering.
[Probably short for Medieval Latin crux (interpretum), torment (of interpreters), from Latin crux, cross.]
- predicational
- predicative
- predicatively
- predicatory
- predict
- predictability
- predictable
- predictably
- prediction
- predictive
- predictively
- predictor
- predigest
- predigestion
- predilection
- predispose
- predisposition
- prednisolone
- prednisone
- predoctoral
- predominance
- predominancy
- predominant
- predominantly
- predominate