In 5th Edition, willpower is modeled by Wisdom as per the core rulebooks.
Wisdom reflects how attuned you are to the world around you and represents perceptiveness and intuition.
According to the Saving Throws table on page 238 of the Dungeon Master's Guide, Wisdom is used for "resisting effects that charm, frighten, or otherwise assault your willpower."PHB chapter 7.
The rules do not use the term "willpower". The closest they come is "will to live" which is for Constitution.
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