This is the 16017th most frequent Polish word.
trzydziestych
"Trzydziestych" means "thirtieth" (plural genitive form) in English.
Here, 'trzydziestych' is used as an ordinal adjective describing the decades of a century.
W trzydziestych latach XX wieku nastąpiło wiele zmian.
In the thirties of the 20th century, many changes occurred.
In this sentence, 'trzydziestych' refers to the decade as a standalone period.
Budynki tej dzielnicy pochodzą jeszcze z trzydziestych.
The buildings in this district date back to the thirties.
Here, 'Trzydziestych' is used as part of a proper name referring to a street.