Greek paradoxos meant contrary to expectation. Merriam-Webster traces it to para-, beyond or outside, and dokein, to think or seem.
Paradoxon and paradoxos are grammatical forms in the same Greek family, not two successive sound changes.
Sources
- Merriam-Webster: paradox
Word History gives the Greek/Latin formation and dokein; Did you know glosses para- as beyond or outside.
- Online Etymology Dictionary: orthodox
Also built on *doxa* "opinion", from *dokein* "to seem": orthodox
- Online Etymology Dictionary · paradox
Meanings of the older forms on the word path.