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"Cómo se llama tu amigo" is a form of "cómo se llama tu amigo", a phrase which is often translated as "what your friend's name is". "El monstruo" is a form of "monstruo", a noun which is often translated as "monster". Learn more about the difference between "cómo se llama tu amigo" and "el monstruo" below.
cómo se llama tu amigo(    
koh
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moh
seh
yah
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mah
too
ah
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mee
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goh
)A phrase is a group of words commonly used together (e.g., once upon a time).
1. (informal) (in sentences; singular)
A word or phrase used to refer to the second person informal “tú” by their conjugation or implied context (e.g., How are you?).
a. what your friend's name is 
Dime por favor cómo se llama tu amigo. ¡Es muy guapo!Please tell me what your friend's name is. He's so handsome!
2. (informal) (in questions; singular)
A word or phrase used to refer to the second person informal “tú” by their conjugation or implied context (e.g., How are you?).
a. what's your friend's name 
¿Cómo se llama tu amigo? No no has presentado.What's your friend's name? You haven't introduced us.
el monstruo(
mohns
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trwoh
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
a. monster 
Los habitantes de las montañas de por aquí hablan de un monstruo que aparece cuando nieva: el yeti.The people who live in the mountains around here speak of a monster that appears when it snows: the yeti.
a. monster 
No pongas esa cara, que mi amiga no es un monstruo.Don't look at me like that; my friend isn't a monster.
a. monster 
La persona que abandonó esta camada de cachorros es un monstruo.Whoever abandoned this litter of puppies is a monster.
a. freak 
El hombre de dos cabezas era el monstruo más famoso del circo.The two-headed man was the most famous freak in the circus.
a. monster 
Ese puente es un monstruo; pesa más de 7,000 toneladas.That bridge is a monster; it weighs over 7,000 tons.
6. (marvel)
a. giant 
Este monstruo del patinaje sobre hielo ganó la medalla de oro cinco años seguidos.This ice-skating giant won the gold medal five years in a row.
b. phenomenon 
Se le considera a Patrick un monstruo del mundo de los negocios.Patrick is considered a phenomenon in the world of business.
7. (colloquial) (genius)
A word or phrase that is commonly used in conversational speech (e.g., skinny, grandma).
a. whizz  (colloquial)
A word or phrase that is commonly used in conversational speech (e.g., skinny, grandma).
Mi mejor amigo es un monstruo de las matemáticas.My best friend is a math whizz.
An adjective is a word that describes a noun (e.g., the big dog).
8. (colloquial) (brilliant)
A word or phrase that is commonly used in conversational speech (e.g., skinny, grandma).
a. fantastic  (colloquial)
A word or phrase that is commonly used in conversational speech (e.g., skinny, grandma).
Me parece una idea monstruo.I think it's a fantastic idea.