This is the 5007th most frequent Polish word.
poranku
"Poranku" means "morning" (in the genitive or locative case).
'Poranku' here is used as a locative singular form of 'poranek', indicating the time of the morning in which the action occurred.
Wczoraj o poranku wstałem wcześnie.
Yesterday in the morning, I woke up early.
'Poranku' is again in the locative case and conveys a general sense of the morning as a time period.
Nic nie jest pewne o poranku.
Nothing is certain in the morning.
'Poranku' is used to specify the timing of an upcoming event, similarly in the locative case.