unbuttoned, unfastened
Ella no notó que uno de sus botones se desabrochó.
She didn't notice that one of her buttons had come undone.
Después me desabrochó la blusa.
Then he unbuttoned my blouse.
— El conformista (1971)
Se desabrochó los pantalones.
He unbuttoned his pants.
Tom se desabrochó su chaqueta.
Tom unbuttoned his jacket.