You seriously need a better dictionary.
Irony:
1. The use of words to express something different from and often opposite to their literal meaning.
2. An expression or utterance marked by a deliberate contrast between apparent and intended meaning.
3. A literary style employing such contrasts for humorous or rhetorical effect.
Conundrum:
1. A riddle in which a fanciful question is answered by a pun.
2. A paradoxical, insoluble, or difficult problem; a dilemma: ?the conundrum, thus far unanswered, of achieving full employment without inflation? (Arthur M. Schlesinger, Jr.).
Paradox:
1. A seemingly contradictory statement that may nonetheless be true: the paradox that standing is more tiring than walking.
2. One exhibiting inexplicable or contradictory aspects: ?The silence of midnight, to speak truly, though apparently a paradox, rung in my ears? (Mary Shelley).
3. An assertion that is essentially self-contradictory, though based on a valid deduction from acceptable premises.
4. A statement contrary to received opinion.