Surely, it'd be "reaction". But just for the heck of it, is not a "reaction" a type of action?
I've been pondering something like that, but no, there is only reaction, there is something about presence which tells me in some instances at least, that presence is action, and it is constant, if we are considering the context we inhabit. So the physcial world shapes us both as individuals as well as species. The physical world is the dominient presence, and that presence is action, for lack of a better word. It is to this we must respond, it is to this, we like every other organism must react to, there is no such thing as action in the strict sense of the word. Perhaps this reality holds on a diminishing scale, do not bacteria react in response to the greater presence of a host body? Just a thought, still feeling my way here. Oh again, your above statement, action infers cause, where in fact the physcial world is cause, as something which triggers a reactionary response. The physcial world is our object, our reaction/experience of object is the said relation between subject and object, and thus it is apparent reality.