This is the 82nd most frequent Dutch word.
hele
"Hele" means "whole" or "entire" in English.
In this sentence, "hele" modifies the noun "dag" (day) to indicate completeness or entirety.
De hele dag regende het.
It rained the whole day.
Here, "heel" (a derivative of "hele") functions as an adverb to intensify the adjective "verbaasd" (surprised).
Ze was heel verbaasd over het nieuws.
She was very surprised about the news.
In this instance, "hele" emphasizes that the noun "taart" (cake) was consumed in its entirety.