La familia

Almost every family word in Spanish comes twice: hijo and hija, hermano and hermana, tío and tía, abuelo and abuela. Learn one and the other costs you a single letter.

Then the plural does something English has no equivalent for.

One boy makes the whole group masculine

Hermanos is brothers. It is also brothers and sisters together. Four sisters and one brother are hermanos, and so are two brothers. The masculine plural is the default for any mixed group, however lopsided.

This means padres is not fathers, it is parents. Hijos is children, not sons. Tíos is aunts and uncles. Native speakers are not being careless; the form genuinely carries both meanings, and context does the rest.

Some Spanish speakers now write hermanos y hermanas to be explicit, in the same way English writers reach for they. It is a live argument and you can stay out of it.

tio does not have to be your uncle

In Spain, tío and tía are also what you call a friend, or anyone at all. ¿Qué pasa, tío? is what is up, mate. It is completely ordinary among people under about fifty, and completely absent from Latin American Spanish, where the word stays firmly in the family.

esposa, mujer, senora

Three words for a wife, and they are not interchangeable. Esposa is neutral and slightly formal. Mujer is woman and wife both, so mi mujer is my wife and is the commonest thing to say in Spain. Señora is a married woman generally, and as a form of address it is madam.

The mirror image is worse. Marido is husband. Hombre is not husband, and mi hombre will not be understood the way mi mujer is. The symmetry breaks, and no rule explains why.