Beyond what is normal or natural.
"The boy's sixty page essay on contractual efficacy was precociously preternatural."
Existing outside of nature.
"The Japanese automaton was intriguingly preternatural."
Inexplicable by ordinary means
"Saitama's strength is preternatural."
"Beyond or different from what is natural," 1570s, from Medieval Latin preternaturalis (mid-13c.), from Latin phrase praeter naturam (praeterque fatum) "beyond nature (and beyond fate)," from praeter "beyond, over, more than in quantity or degree" (see preter-) + accusative of natura "nature" (natural).