essential amino acid

Main Entry: essential amino acid
Function: noun
: any of various alpha-amino acids that are required for normal health and growth, are either not manufactured in the bodyor manufactured in insufficient quantities, are usually supplied by dietary protein, and in humans include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, andvaline

essential amino acid n.
An alpha-amino acid that is required for protein synthesis but cannot be synthesized by humans and must be obtained in the diet.