How to Say "decease" in Spanish
The Spanish word for “decease” is “fallecimiento” — B2 level.

Examples
Lamentamos informar el fallecimiento del reconocido actor.
We regret to inform you of the passing of the well-known actor.
La familia anunció el fallecimiento a través de las redes sociales.
The family announced the death through social media.
Necesitamos el acta de fallecimiento para completar el trámite.
We need the death certificate to complete the paperwork.
A Formal Alternative
Think of this word as the formal equivalent to 'muerte.' Use it when you want to be respectful, like in a letter or a news report.
It is a Masculine Noun
Since it ends in -o, it is masculine. Use 'el' or 'un' with it: 'el fallecimiento,' never 'la fallecimiento.'
Fallecimiento vs. Fallo
Mistake: “Using 'fallo' to mean death.”
Correction: Use 'fallecimiento' for death. 'Fallo' usually means a 'mistake' or a 'legal ruling.'
Usage with Pets
Mistake: “Using 'fallecimiento' for a dog or cat.”
Correction: While understandable, it sounds very strange. For animals, it's better to use 'muerte' (death).
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