#atomic mass

• Now (dialectal) — In popular and regional Romanian (specific to the Moldavian and Transylvanian dialects), a time adverb meaning 'now', 'at this moment', or 'immediately'; in physics and chemistry (as an international acronym often written 'amu'), it represents the atomic mass unit, structurally defined as one-twelfth of the mass of a carbon-12 atom.
• Antisubstance — A hypothetical or experimental form of matter composed entirely of antiparticles (such as antiprotons, antineutrons, and positrons), representing the structural inverse equivalent of ordinary matter. Upon direct contact between a substance and an antisubstance, the physical process of total annihilation occurs, instantly converting the entire mass of both entities into pure energy in the form of high-intensity gamma rays.