thir ‧ ty /ˈθɜːti $ ˈθɜːrti/ BrE AmE number
[ Language: Old English ; Origin: thritig , from thrie 'three' ]
1 . the number 30
2 . the thirties ( also the '30s, the 1930s [plural] ) the years from 1930 to 1939:
In the thirties, air travel really began to take off.
the early/mid/late thirties
The family sold the house in the early thirties.
3 . be in your thirties to be aged between 30 and 39
early/mid/late thirties
She must be in her early thirties by now.
4 . in the thirties if the temperature is in the thirties, it is between 30 degrees and 39 degrees
in the low/mid/high thirties
a hot day, with temperatures in the low thirties
—thirtieth adjective , pronoun :
her thirtieth birthday
I’m planning to leave on the thirtieth (=the 30th day of the month) .