How to Say "first letters" in Spanish
The Spanish word for “first letters” is “iniciales” — A2 level. This is a very common word in everyday Spanish.
English → SpanishA2
nounA2
the beginning letters of words in a title or acronym

Examples
Por favor, escribe tus iniciales en cada página del contrato.
Please, write your initials on every page of the contract.
Las iniciales de su nombre están bordadas en la camisa.
The initials of his name are embroidered on the shirt.
Always Feminine
Even though it ends in '-es', this noun is always feminine because it comes from 'la inicial'. Use 'las iniciales'.
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