Irony, oxymoron and now paradox. These are related terminologies and irony is a part of both oxymoron and paradox but as literary devices these two vary.
In Shakespeare's play Timon of Athens the character Timon learns: 'nothing brings me all things' (V.ii.73) and at first it may appear confusing and contradictory but it eventually strikes the reader or listener or audience as one bearing an underlying message or a concept or a philosophy. And this literary device is a paradox, where a whole phrase or sentence carries a contradiction or would irony, unlike an oxymoron where a pair of words bearing opposite meanings are used, but those convey one thing without being ambiguous.
In Timon of Athens, Timon's statement could convey that nothing and infinity are cyclical or that less is more. Yes, less is more, too is a paradox.