This is the 17205th most frequent Polish word.
zagadka
"Zagadka" means "riddle" or "mystery."
In this sentence, 'zagadka' is used in its meaning of a puzzle or riddle that requires solving.
Rozwiązałem trudną zagadkę.
I solved a difficult riddle.
Here, 'zagadka' refers to a mystery or enigmatic situation that required investigation.
Jego zagadka została rozwiązana przez detektywa.
His mystery was solved by the detective.
In this usage, 'zagadka' is metaphorically likened to a complex or intricate situation.