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"Gentío" is a noun which is often translated as "crowd", and "multitud" is a noun which is also often translated as "crowd". Learn more about the difference between "gentío" and "multitud" below.
el gentío(
hehn
-
tee
-
oh
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
la multitud(
mool
-
tee
-
tood
)A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
1. (throng)
a. crowd 
El músico callejero atrajo a una gran multitud.The street musician attracted a big crowd.
Hay una multitud afuera del teatro esperando a que salga la actriz.There's a crowd outside the theater waiting for the actress to come out.
b. multitude 
El ladrón escapó y se perdió entre la multitud.The thief ran away and got lost in the multitude.
2. (myriad)
a. multitude 
Tu receta está en algún lugar entre esta multitud de papeles.Your prescription is somewhere along this multitude of papers.
b. ton 
Tengo una multitud de reportes que hacer para mañana.I have a ton of reports to fill for tomorrow.
c. dozens 
Entré a su dormitorio y vi una multitud de libros dispersos por el piso.I entered his room and saw dozens of books on the floor.