Seal: fasten or close securely.
"he folded it, sealed the envelope, and walked to the mailbox"
synonyms: fasten, secure, shut, close, lock, bolt More
"she quietly sealed the door behind her"
stop up, seal up, make airtight/watertight, cork, stopper, plug
"seal each bottle while it is hot"
prevent something from escaping by closing a container or opening.
Block (as in blockchain) - A blockchain is a digitized, decentralized, public ledger of all cryptocurrency transactions. Originally developed as the accounting method for the virtual currency Bitcoin, blockchains – which use what's known as distributed ledger technology (DLT) – are appearing in a variety of commercial applications today.