From permission +‎ -less.

permissionless (not comparable)

1. Without permission.
   • 2023 May 26, Rand Hindi, “How Homomorphic Encryption Can Make Blockchain Private”, in Forbes‎^[1], New York, N.Y.: Forbes Media, →ISSN, →OCLC, archived from the original on 12 June 2023:

     And this is what makes FHE a great solution for blockchain privacy: By keeping the on-chain data encrypted, we can have decentralized, permissionless blockchains where everything is on-chain and auditable while not actually visible.

• impressionless