Amino acid Meaning of Amino acid One of several molecules that join together to form proteins. There are 20 common amino acids found in proteins. Also See: Alveolar soft part sarcoma Antibody-dependent cell-mediated cytotoxicity Antineoplaston Heart Rate Anesthetic Enzymes Auditory Aspiration Asymptomatic inflammatory prostatitis Angioplasty ALSO SEE: Aspirate