This is the 2982nd most frequent Polish word.
odpoczynku
"Rest" or "repose."
Here, 'odpoczynku' is used in the genitive case to indicate an object that is needed.
Potrzebuję trochę odpoczynku po długim dniu.
I need some rest after a long day.
In this sentence, 'odpoczynku' is used in the genitive case in a subordinate clause to denote possession of 'czas' (time).
Czas odpoczynku jest ważny dla zdrowia.
Rest time is important for health.
The word 'odpoczynku' is in the genitive case due to the negative structure and qualifies the noun 'chwili' (moment).