Mort vs. défunt vs. décédé

In French, the words 'mort', 'défunt' and 'décédé' all refer to the state or condition of being dead. However, they are used in different contexts and have nuanced meanings that affect how they are used in sentences.

Mort

'Mort' is a noun or an adjective directly translating to 'dead'. It describes the state of death in a general and straightforward manner.
La reine est morte, vive le roi !
(The queen is dead, long live the queen!)
La souris est morte.
(The mouse is dead.)

Défunt

'Défunt' is a noun or an adjective usually used in a formal context to refer to someone who has passed away. It often carries a respectful tone.
Le défunt roi était aimé de tous.
(The late king was loved by all.)
Ils ont rendu visite à la tombe du défunt.
(They visited the grave of the deceased.)

Décédé

'Décédé' is a formal term used mainly in administrative, legal or formal contexts to refer to someone who has died.
Le certificat indique que la personne est décédée.
(The certificate indicates that the person is deceased.)
La liste comprenait le nom des personnes décédées dans l'accident.
(The list included the names of people who died in the accident.)

Summary

'Mort', 'défunt' and 'décédé' all refer to death, but they are used differently. 'Mort' is used in a general sense, 'défunt' refers respectfully to someone who has died, and 'décédé' appears in more formal or legal contexts.