connaturalizar

A rare, mostly philosophical and theological verb: to become so accustomed to something that it turns into second nature (used almost always reflexively, connaturalizarse con algo). It appears in translations of scholastic philosophy and academic prose, essentially never in everyday speech.

• Con los años se connaturalizó con la vida en el monasterio. — Over the years he became so used to monastery life that it felt like second nature.
• El filósofo explica cómo el hábito connaturaliza la virtud en el alma. — The philosopher explains how habit makes virtue second nature in the soul.
• Le costó connaturalizarse con las costumbres del nuevo país. — It took him a while for the new country's customs to feel natural to him.

So rare that a learner will essentially never need to produce it — acostumbrarse a covers the everyday sense of "getting used to something."

Often confused with acostumbrar.