Bütün and hepsi may be used for the same meaning, meaning "all". Hepsi means directly "all (of)" Bütün çiçekler - all the flowers Çiçeklerin hepsi - all of the flowers Bütün gün - the whole day, all day long More specificly bütün can be used directly for "the whole", "the entire". when something is made up of shares that constitute the whole. I hope this helps.

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