Describes someone or something that is prone to change.
Su carácter voluble le hacía difícil mantener amistades duraderas, ya que cambiaba de opinión constantemente.
His fickle nature made it hard for him to maintain lasting friendships, as he constantly changed his mind.
Su opinión es voluble, ya que cambia frecuentemente dependiendo de la situación y de las personas que la rodean.
Her opinion is changeable, as it frequently shifts depending on the situation and the people around her.