This is the 12027th most frequent Polish word.
leku
"Leku" is the genitive or dative singular form of "lek," meaning "medicine" or "drug" in Polish.
In this sentence, 'leku' refers to the medicine in a partitive context, indicating the object of purchase.
Mam potrzebę kupienia tego leku.
I feel the need to purchase this medicine.
'Leku' here refers to medicine as the object of the search, used in the genitive singular form due to negation.
Nie znaleźliśmy żadnego leku na tę chorobę.
We could not find any medicine for this illness.
Here 'leku' appears as the object in the locative case, indicating the means by which the patient experiences improvement.