A puzzle or difficulty.
The basic, central, or essential point or feature.
The critical or transitional moment or issue, a turning point.
The hardest point of a climb.
A cross on a coat of arms.
An affair, condition, or subject, especially one of concern or (especially when preceded by the) one that is problematic.
Matter made up of normal particles, not antiparticles.
Aristotelian: undeveloped potentiality subject to change and development; formlessness. Matter receives form, and becomes substance.
The basic structural component of the universe, usually having mass and volume.
An approximate amount or extent.
Printed material, especially in books or magazines.
A kind of substance.
To be important.
To care about, to mind; to find important.