Lettera vs. missiva
In Italian, both lettera and missiva can be translated as letter. However, they are not interchangeable, as they belong to different language registers and are used in distinct contexts.
Lettera
A1This is the standard, common, and all-purpose word for a letter. It is used in everyday conversation and writing for any kind of written message sent to someone, whether it's personal, commercial, formal, or informal.
Ho scritto una lettera a mia nonna per il suo compleanno.
(I wrote a letter to my grandmother for her birthday.)
L'azienda mi ha inviato una lettera di assunzione.
(The company sent me a job offer letter.)
Hai messo un francobollo sulla lettera prima di spedirla?
(Did you put a stamp on the letter before mailing it?)
Il postino ha appena consegnato una lettera per te.
(The mail carrier just delivered a letter for you.)
Ho trovato una vecchia lettera d'amore in soffitta.
(I found an old love letter in the attic.)
Dobbiamo scrivere una lettera di reclamo al servizio clienti.
(We have to write a letter of complaint to customer service.)
Missiva
C1This is a formal, high-register, and somewhat literary or bureaucratic term for a letter. It often implies a communication of particular importance, officiality, or solemnity. You would not use missiva in a casual conversation but would encounter it in historical texts, legal contexts, formal journalism, or literature.
L'ambasciatore ha consegnato una missiva urgente al ministro.
(The ambassador delivered an urgent missive to the minister.)
Nello studio dello storico fu ritrovata una missiva del Seicento.
(A missive from the 17th century was found in the historian's study.)
L'avvocato ha inoltrato una missiva formale alla controparte.
(The lawyer forwarded a formal missive to the opposing party.)
Il giornale ha pubblicato il contenuto della missiva papale.
(The newspaper published the content of the papal missive.)
Quella criptica missiva annunciava un cambiamento imminente.
(That cryptic missive announced an imminent change.)
La spia attendeva una missiva con le nuove istruzioni.
(The spy was waiting for a missive with the new instructions.)
Summary
In essence, the main difference is the register. Lettera is the neutral, everyday word you will always use for a letter in almost any situation. Missiva is a formal and elevated alternative, reserved for official, historical, or particularly solemn communications, and is rarely used in modern spoken Italian.