How does Spanish say 'each other'?

It uses the plural reflexive pronouns nos, os, se with a plural subject. Nos vemos means 'we see each other', os ayudáis 'you help each other', se quieren 'they love each other'. There is no separate word for 'each other' - the reciprocal meaning is carried by the reflexive pronoun plus a plural subject. If you need to remove ambiguity, add el uno al otro (masculine) / la una a la otra (feminine) or mutuamente.

What is the difference between reflexive and reciprocal se?

Reflexive means the subjects act on themselves; reciprocal means they act on each other. Los niños se lavan can mean 'the children wash themselves' (reflexive) or 'the children wash each other' (reciprocal) - only context or a clarifier tells them apart. For 'themselves', add a sí mismos (se hablan a sí mismos, they talk to themselves); for 'each other', add el uno al otro (se hablan el uno al otro, they talk to each other). The reciprocal reading needs a plural subject; the reflexive works with any number.

How do you make a reciprocal sentence unambiguous in Spanish?

Add el uno al otro, la una a la otra, los unos a los otros (one another) or the adverb mutuamente (mutually) to force the reciprocal reading: se ayudan el uno al otro (they help one another), se respetan mutuamente (they respect each other). The a inside el uno al otro changes to match the verb's preposition - se acuerdan el uno del otro (they remember each other), because acordarse takes de. To force the reflexive 'themselves' reading instead, use a sí mismos.

Reciprocal Verbs: saying "each other"

When two or more people do something to each other - love, help, look at, write to, understand - English adds "each other" or "one another". Spanish does not need an extra phrase: it reuses the reflexive pronouns nos, os, se, and lets a plural subject do the rest.

Nos ayudamos. (We help each other.)
Os conocéis. (You two know each other.)
Se quieren. (They love each other.)

This is the reciprocal use of the reflexive. It only works with a plural subject, for the obvious reason that it takes at least two to be reciprocal.

The reciprocal pronouns

Only the plural reflexives can be reciprocal, because reciprocity needs more than one person:

Subject	Pronoun	Example
nosotros/-as	nos	nos escribimos (we write to each other)
vosotros/-as	os	os ayudáis (you help each other)
ellos/ellas/Uds.	se	se miran (they look at each other)

Nos vemos mañana. (We'll see each other tomorrow.)
Se abrazaron al llegar. (They hugged each other on arriving.)
¿Os habláis todavía? (Do you two still talk to each other?)

Reciprocal vs reflexive: the ambiguity

A plural reflexive sentence can, in principle, mean two things:

Los niños se lavan.
- Reflexive: The children wash themselves.
- Reciprocal: The children wash each other.

Most of the time context settles it - se quieren almost always means "they love each other", not "they love themselves". But when it genuinely matters, Spanish adds a clarifier.

Forcing the reciprocal: el uno al otro / mutuamente

To make "each other" unmistakable, add el uno al otro (one another) or the adverb mutuamente:

Se ayudan el uno al otro. (They help one another.)
Se respetan mutuamente. (They respect each other.)
Las dos hermanas se cuidan la una a la otra. (The two sisters look after each other.) - feminine, la una a la otra.
Se necesitan los unos a los otros. (They need one another.) - more than two, plural.

The little phrase agrees in gender and number with the people, and its a changes to match the verb's preposition: with acordarse de, it becomes el uno del otro - se acuerdan el uno del otro (they remember each other).

Forcing the reflexive: a sí mismos

To force the "themselves" reading instead, add a sí mismos / a sí mismas:

Se engañan a sí mismos. (They deceive themselves.)
Solo se quieren a sí mismos. (They only love themselves.)

So el uno al otro pins down "each other"; a sí mismos pins down "themselves".

The verbs that turn reciprocal easily

Verbs about relationships and communication slip into the reciprocal most naturally - because these are things people do mutually:

quererse, amarse (to love each other)
conocerse (to know / meet each other)
verse (to see each other)
hablarse, escribirse, llamarse (to talk / write / call each other)
ayudarse, apoyarse (to help / support each other)
mirarse, abrazarse, besarse (to look at / hug / kiss each other)
pelearse, odiarse (to fight / hate each other)
entenderse, respetarse (to understand / respect each other)
Se conocieron en la universidad. (They met each other at university.)
Nos llamamos todos los días. (We call each other every day.)
Aunque discuten, se apoyan siempre. (Even though they argue, they always support each other.)

Worked examples

Se escriben cartas cada semana. (They write letters to each other every week.)
Nos entendemos sin hablar. (We understand each other without speaking.)
Los dos rivales se odiaban mutuamente. (The two rivals hated each other.)
Se dieron la mano el uno al otro. (They shook hands with each other.)
Prometieron ayudarse siempre. (They promised to help each other always.)
Al principio no se caían bien, pero acabaron queriéndose. (At first they didn't like each other, but they ended up loving each other.)

Common mistakes English speakers make

Trying to translate "each other" as a word. There is no single Spanish word for it. The reciprocal meaning lives in the plural reflexive pronoun - se, nos, os - plus a plural subject. Say se ayudan, not "se ayudan cada otro".

Using it with a singular subject. Reciprocity needs at least two people, so the reciprocal requires a plural subject. One person cannot do something "to each other".

Forgetting the pronoun agrees with the subject. It is nos with nosotros, os with vosotros, se with ellos - nos vemos, os veis, se ven. Mixing them (nos ven) breaks the sentence.

Letting a real ambiguity stand. When "themselves" and "each other" would mean genuinely different things, add the clarifier: se miran el uno al otro (at each other) versus se miran a sí mismos (at themselves, e.g. in a mirror).

Reuse the reflexive pronoun, keep the subject plural, and reach for el uno al otro or mutuamente when you need to be crystal clear. That is the whole of the reciprocal in Spanish.