This is the 11212th most frequent Polish word.
gruby
"Gruby" means "fat" or "thick" in English.
'Gruby' is used in a metaphorical sense here, referring to the severity of a mistake.
Ewa popełniła gruby błąd w pracy.
Ewa made a serious mistake at work.
Here, 'gruby' describes the thickness of the sweater, emphasizing its suitability for cold weather.
Kupiłem gruby sweter na zimę.
I bought a thick sweater for winter.
In this case, 'gruby' refers to someone's weight, indicating that the person is overweight.