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"Pechos" is a form of "pecho", a noun which is often translated as "chest". "Busto" is a noun which is often translated as "bust". Learn more about the difference between "busto" and "pechos" below.
el busto()
A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
el pecho()
A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).