This question arose last night and wasn't fully resolved. A pet was purchased from the Menagerie (City Expansion) called the Stinker. The card says:
Instead of attacking an enemy, the player may move that enemy one square clockwise or counter-clockwise.
Now I'm paraphrasing a little as I don't have the card with me, but it definitely said "attacking" and the interpretation of what constitutes an "attack" was disputed. Does this card mean any enemy encountered, or only one which was already on a square when the player moved in to that square?
The one argument here is that if you encounter a square and flip over an adventure card with an enemy, you are "defending" against it rather than "attacking" it and the Stinker is unplayable against it.
The counter-argument is that in any battle the two combatants are "attacking" each other, so the card is playable. It raises the question of whether an "attack" is only considered such from the point of view of the instigator, or if "attack" is essentially just any form of combat.