This is the 7186th most frequent Polish word.
jakuba
"Jakuba" is the genitive form of the Polish name "Jakub," which translates to "Jacob" in English.
Here, 'Jakuba' is the accusative case of the name Jakub, used as the object of the verb 'widzieć' (to see).
Jakuba widziałem wczoraj na rynku.
I saw Jakub yesterday at the market.
In this sentence, 'Jakuba' is the genitive case, indicating the absence of Jakub from home.
Nie ma Jakuba w domu.
Jakub is not at home.
Here, 'Jakuba' is used in the genitive case to indicate possession, referring to a book belonging to Jakub.