The word "contraption" actually comes from the Old French word "contrapcion," which itself derives from the Latin "contraptio," meaning "a seizing or grasping."
Therefore, "contraption" originally referred to something that held or held together parts, later evolving to mean a device or mechanism, especially one that is oddly constructed or makeshift.
While "con" is part of the etymology, it doesn't carry its typical meaning of "against" or "together" in "contraption."