“Attack a target” vs taking the Attack action in regards to Hound of Ill Omen

I have a few questions regarding what falls under the category of "attacking [the Hound of Ill Omen’s] target" for the Shadow Sorcerer’s Hound of Ill Omen feature.

…On its turn, [the Hound of Ill Omen] can move only toward its target by the most direct route, and it can use its action only to attack its target." (XGE p. 51)

So the hound is limited to using its action to attack its target. But does "attacking its target" specifically mean taking the Attack action to make an attack roll, or are their other things that qualify as an attack?

For example, could the hound use the Attack action to attempt to shove or grapple a creature? Or, stretching it a bit further, could they take an action (that is not the Attack action) to attempt to damage their target; (for example using the special action granted by the Dragon’s Breath spell) or if attack were impossible given the hound and the target’s positions taking the Dash action to be able to make a future attack possible?

Furthermore, would a hound be free to use its bonus action however it wants? For example, if Expeditious Retreat were cast on the hound, could it use the Dash action as a bonus action even though it is not attacking the target?

Thank you in advance for any answers I might receive.