Medical Definition of start codon
: a genetic codon in messenger RNA that stimulates the binding of a transfer RNA which starts protein synthesis <… the AUG codon for methionine functions as the start codon in the vast majority of mRNAs.—Harvey Lodish et al., Molecular Cell Biology, 6th edition, 2007>—called also initiation codon; compare stop codon
Seen and Heard
What made you want to look up start codon? Please tell us where you read or heard it (including the quote, if possible).