1. a specific sequence of three adjacent nucleotides on a strand of DNA or RNA that specifies the genetic code information for synthesizing a particular amino acid
The Collaborative International Dictionary of English v.0.48:
Codon \Co"don\ (k[=o]"d[o^]n), n. (Molecular biology)
a sequence of three nucleotides in a genome or a DNA or
messenger RNA molecule, which specifies the incorporation of
one amino acid or is a stop signal, during the biosynthesis
of proteins. Codons occur within the protein-coding segments
of the DNA or RNA genome of living organisms. The amino acid
sequence of proteins synthesized on ribosomes is thus
determined by the sequence of the nucleotides in the genome.
Note: Outside of coding regions, there is no direct
correspondence of the nucleotide sequence with protein
sequence, and certain signalling functions of nucleic
acids are not specified by three-nucleotide codons.
Certain types of polypeptide synthesized in living
organisms are not synthesized on ribosomes, and the
sequences of these polypeptides do not have a
corresponding nucleotide sequence in the genome.
WordNet (r) 3.0 (2006):
n 1: a specific sequence of three adjacent nucleotides on a
strand of DNA or RNA that specifies the genetic code
information for synthesizing a particular amino acid