During my first extended visit to Mexico, I went to a party and talked to a guy who had introduced himself as Salvador. The next day I ran into a mutual friend who had also been at the party. He mentioned that he saw me talking to Chava. I had recently learned that chava means girl, so I told him that I hadn’t talked to una chava at the party. So he laughed and set me straight: Chava is a nickname for Salvador, a man’s name.
Frutos Prohibidos, Condesa neighborhood, Mexico City
Just as in English, where we can say Bob for Robert or Sue for Susan, many names in Spanish have accepted variants. Some nicknames are formed simply by chopping off the end (Mauricio → Mau, Fernando/a →Fer, Victor →Vic) or by adding a diminutive suffix (Miguel → Miguelito). Others are not so transparent. It is helpful to be prepared for the most common ones.
Nicknames in Spanish
People with two nombres can use nicknames for both: José Antonio → Pepe Toño.
The situation with names and nicknames presents a special challenge for learners. As you can see from my anecdote above, many people will introduce themselves with their given name (their nombre de pila) rather than with the name you’ll hear later. If you don’t know the standard name-nickname associations, you can easily get lost.
If you don’t know whether someone uses a nickname, you can always ask: Oye, ¿te dicen Lalo? ¿O prefieres que te digan Eduardo?
Me dicen Lalo
Consider this conversational exchange.
— ¿Cómo te dicen?
— Pues me llamo Eduardo pero mis amigos me dicen Lalo. My name is Eduardo but my friends call me Lalo.
From this example, you can see that llamar is used for the name and decir is used for the nickname. Note that decir, not llamar, translates as call here.
Ser is also possible: Me llamo ______ pero soy ______ para los cuates. (telenovela dialogue)
There isn’t a well-established word for nicknames. Most people will simply say A los Guillermos les dicen Memo. Apodos or sobrenombres normally describe some physical or psychological trait. El Greñitas might stick for a little kid with crazy hair. Gangsters and celebrities often get apodos as well: El Chapo (from chaparro, shortie), La Tigresa (the tigress). Note the use of the definite article.
Nombres de cariño
A nombre de cariño is a pet name you call your lover: (mi) amor, (mi) vida, cosita, gordito/a, flaco/a, nene/a (baby), peque (from pequeño, child).
To show either affection or contempt, the definite article can be used before a person’s name or nickname when you are referring to them in the third person: Ayer me vi con la Tatis (from Tatiana). ¡Ojo! Not everyone does this. Check first whether this usage is common among your social circle before trying it out.
Naming a baby
For talking about naming a baby, the verb you want is poner.