A labyrinth disk for a turbomachine is provided. The disk includes a hub, a web and a frustoconical peripheral portion, having on one face labyrinth seal teeth and on the other face radial ribs. The flanks of the ribs delimit, between one another, channels which open out at the periphery of the disk. The width of the channels decreases from the base of the frustoconical portion to the opening at the periphery. The ribs are split close to the periphery, and a recess is created between the two flanks of one and the same rib.