astreñir

A rare, essentially obsolete verb the dictionary defines simply as a synonym of astringir — to tighten or constrict, and by extension to bind or oblige someone to do something. No modern speaker uses astreñir in practice; even astringir itself is a fairly technical/medical word, and astreñir has all but vanished in its favor.

• En textos antiguos, astreñir significaba lo mismo que astringir. — In old texts, astreñir meant the same as astringir.
• El deber lo astreñía a cumplir su promesa. — Duty bound him to keep his promise.
• Hoy nadie diría astreñir; se usa astringir o constreñir. — Today no one would say astreñir; people use astringir or constreñir.

Trying to use astreñir in modern writing — it will read as an error or an obscure archaism rather than a real stylistic choice, since even native speakers wouldn't recognize the form.

Often confused with astringir.