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"La correa" is a form of "correa", a noun which is often translated as "strap". "Arnés" is a noun which is often translated as "harness". Learn more about the difference between "arnés" and "la correa" below.
el arnés(
ahr
-
nehs
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
a. harness 
Por seguridad, tienes que usar un casco y un arnés para escalar.For safety reasons, you must wear a helmet and a harness to climb.
a. armor  (United States)
Regionalism used in the United States
La flecha no pudo penetrar el arnés del caballero.The arrow couldn't penetrate the knight's armor.
b. armour  (United Kingdom)
Regionalism used in the United Kingdom
El arnés y el escudo protegieron al guerrero de las espadas enemigas.The armour and the shield protected the warrior from the enemy swords.
la correa(
koh
-
rreh
-
ah
)A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
1. (band)
d. strop  (to sharpen razor)
El barbero afiló su navaja en la correa antes de empezar a afeitarme la barba.The barber sharpened his razor on the strop before he started to shave my beard.
2. (clothing)
a. belt 
Si no me pongo correa, se me caen los pantalones.If I don't wear a belt, my pants fall down.
3. (mechanics)
a. belt 
El mecánico cambió la correa del ventilador de mi auto.The mechanic changed the fan belt on my car.
4. (endurance)
a. patience 
Sonia ha tenido mucha correa con las burlas de sus compañeros.Sonia has had a lot of patience with her colleagues' teasing.