alpha (name of the Greek letter Α, α) / the beginning; the origin of something

(physics) alpha particle (positively charged nucleus of a helium-4 atom)

(astronomy) Alpha Centauri (brightest star in the southern constellation of Centaurus)

(grammar) alpha privative (the prefix a- expressing negation or absence)

(biochemistry) alpha-amino acid (any amino acid that has the amino and carboxylic functional groups attached to the same carbon atom)

(biochemistry) alpha helix (secondary structure found in many proteins)

alphaherpesvirus (any of the subfamily Alphaherpesvirinae of DNA viruses)

(pharmacology) alpha-blocker (drug which blocks α1-adrenergic receptors)

(computer graphics) alpha channel (value indicating level of transparency)

(physics) alpha radiation (radiation of alpha particles)