equivalent to the sum of six and seven; one more than twelve, or seven less than twenty; 13:thirteen miles awaya rise of 13 per centthirteen of the bishops voted against the motion (Roman numeral: xiii or XIII)
a size of garment or other merchandise denoted by thirteen.
thirteen years old:two boys aged eleven and thirteen
Old Englishthrēotīene(see three, -teen). The spelling with initial thi- is recorded in late Middle English
thirteen in other Oxford dictionaries
Definition of thirteen in the US English dictionary