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"Tweet" is an intransitive verb which is often translated as "piar", and "twit" is a noun which is often translated as "el/la imbécil". Learn more about the difference between "tweet" and "twit" below.
tweet(
twit
)An intransitive verb is one that does not require a direct object (e.g., The man sneezed.).
1. (to chirp)
a. piar 
When I awoke, I was lying in a soft bed, and I could hear birds tweeting out the window.Cuando me desperté, estaba acostada en una cama blanda y podía oír a los pájaros piando por la ventana.
b. trinar 
It was early morning. Birds were tweeting in the trees.Era temprano por la mañana. Los pájaros trinaban en los árboles.
2. (computing)
a. tuitear 
I hate how she can't do a thing without tweeting about it.Detesto que no pueda hacer nada sin tuitear sobre ello.
A transitive verb is a verb that requires a direct object (e.g., I bought a book.).
3. (computing)
a. tuitear 
She was banned for tweeting comments that incite hatred.Fue suspendida por tuitear comentarios que incitan al odio.
A noun is a word referring to a person, animal, place, thing, feeling, or idea (e.g., man, dog, house).
4. (computing)
a. el tuit (M)
(m) means that a noun is masculine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
John is totally obsessed with himself, but he doesn't realize that nobody is reading his tweets.John es un ególatra total, pero no se da cuenta de que nadie lee sus tuits.
5. (bird noise)
a. el pío pío (M)
(m) means that a noun is masculine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
The bird landed on the feeder and let out a tweet.El pájaro aterrizó en el comedero y dejó escapar un pío.
d. el gorjeo (M)
(m) means that a noun is masculine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
We could hear the tweets of the birds in the cages as we walked down La Rambla.Oíamos los gorjeos de las aves en las jaulas mientras caminábamos por La Rambla.
twit(
twiht
)A noun is a word referring to a person, animal, place, thing, feeling, or idea (e.g., man, dog, house).
1. (colloquial) (fool) (United Kingdom)
A word or phrase that is commonly used in conversational speech (e.g., skinny, grandma).
Regionalism used in the United Kingdom
a. el imbécil (M), la imbécil (F)
(m) means that a noun is masculine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
(f) means that a noun is feminine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
The toaster's still unplugged, you twit!¡La tostadora todavía no está enchufada, imbécil!
A transitive verb is a verb that requires a direct object (e.g., I bought a book.).
2. (to tease)
a. tomar el pelo 
My buddies kept twitting me about my ugly hat.Mis amigos me seguían tomando el pelo por mi gorra fea.