What is an "oxymoron"? It is a combination of two words used together that have, or seem to have, opposite meanings (Cambridge dictionary).
Here is a poem by Shakespeare, consisting of oxymorons only:
O brawling love! O loving hate!
O anything of nothing first create!
O heavy lightness, serious vanity!
Misshapen chaos of well-seeming forms!
Feather of lead, bright smoke, cold fire, sick health!
Still-waking sleep, that is not what it is!
This love feel I, that feel no love in this.
More oxymorons can be found here: