This is the 252nd most frequent Czech word.
dní
The Czech word "dní" means "days" (genitive plural form).
The word 'dní' is used in the genitive plural form, which follows numbers higher than five in Czech grammar.
Mám dovolenou na sedm dní.
I have a vacation for seven days.
Here, 'dní' is in the genitive plural form, used after the word 'několik' (several) that governs this case.
Uběhlo několik dní od naší poslední schůzky.
Several days have passed since our last meeting.
In this context, 'dní' is part of a time expression, specifically in the genitive plural case, denoting 'of days'.