Is there a term to describe when we put two words together like this, like a reduplication? However, the difference they are two opposites or contradictions?]
For example, this quote here: https://english.stackexchange.com/a/35287
Phrases that combine apparently contradictory ideas are called oxymorons.
If you describe a phrase as an oxymoron, you mean that what it refers to combines two opposite qualities or ideas and therefore seems impossible.
a combination of contradictory or incongruous words (such as cruel kindness)
broadly : something (such as a concept) that is made up of contradictory or incongruous elements