Aces are the spark, the initial energy of the suit: unfocused, undirected, pure and new. So for the Ace of Wands, they are new energy. For the Ace of Swords, a new idea. For the Ace of Cups, a new emotion. For the Ace of Pentacles, new luck (or health).
If we reverse the Aces then the most immediate opposite meaning is that there is no spark of energy, idea, emotion or luck, or that the potential for these is blocked. In the card image, the reversed card shows these aces pointing down, going down, instead of rising up. The overturned cup is emptied of all its liquid.
So what does this mean in a reading? It likely means that the querent should be feeling a stirring of that ace, but isn't. So, the querent should be feel excited at a new prospect or ambition, but doesn't (Ace of Wands reversed). He should feel the start of a new idea, or a new speech he wants to give, but there's nothing (Ace of Swords reversed). He should feel emotions stirring as he, say, gazes at attractive people or his newborn child. But he feels nothing, empty (Ace of Cups reversed). He should feel that his luck is turning, the beginnings of renewed health but doesn't (Ace of Pentacles reversed). The reversed Ace of Pentacles, in addition, could indicate a failed anticipation - the querent anticipated a hint that money would be coming his way, and there's no such hint. Things remain speculative, rather than real and solid.
Reversed Aces are like trying to start a fire, and getting nothing. No smoke, no spark. It's the hope of a hope that never comes. There's not even the feeling that something was there and died - it was never there in the first place. You just feel that something that could have become "it" ought to have been there.
Curious about this card when upright? Go to our Tarot Card Meanings.