thir ‧ teen /ˌθɜːˈtiːn◂ $ ˌθɜːr-/ BrE AmE number
[ Language: Old English ; Origin: threotiene , from thrie , threo % 'three' + tien 'ten' ]
the number 13:
They’ve only sold thirteen tickets so far.
When it happened, I was thirteen (=13 years old) .
—thirteenth adjective , pronoun :
It’s Roberto’s thirteenth birthday.
the thirteenth century
I’m planning to leave on the thirteenth (=the 13th day of the month) .