n.1 the first letter of the Greek alphabet (A).
2 a first-class mark given for a piece of work or in an examination.
3 Astron. the chief star in a constellation.
Phrases and idioms:
alpha and omega the beginning and the end; the most important features. alpha particle (or ray) a helium nucleus emitted by a radioactive substance, orig. regarded as a ray.
Etymology: ME f. L f. Gk