This is the 2529th most frequent Polish word.
obie
"Obie" means "both" (feminine form).
The word 'obie' here is used as a pronoun referring to two feminine entities (sisters) in the nominative case.
Obie siostry poszły na spacer.
Both sisters went for a walk.
The word 'obie' here is used as a numeral pronoun modifying a feminine plural noun 'książki', denoting two specific items.
Kupiliśmy obie książki, które nam polecono.
We bought both books that were recommended to us.
The word 'obie' here is used as a numeral pronoun referring to two feminine entities 'strony' in the nominative case.