When we use the phrase "radical juxtaposition between," we're referring to a significant contrast or pairing of two things that are usually quite different from each other. Some synonyms for this phrase might include stark contrast, extreme juxtaposition, polar opposites, or radical dichotomy. Depending on the context, we might also use terms like radical disparity, unexpected combination, striking dichotomy, or unusual blend. These phrases all convey the same sense of two disparate things being placed next to each other in a way that creates an eye-catching effect and usually invites further reflection or analysis.