This is the 302nd most frequent Hungarian word.
napig
"Napig" means "for [a number of] days" in English.
In this sentence, 'napig' indicates the duration of ten days.
Tíz napig tartott az út.
The trip lasted ten days.
Here, 'napig' expresses a temporal extent of working for days.
Napig szünet nélkül dolgozott.
He worked nonstop for days.
In this context, 'napig' denotes a span of time lasting one day.