To be honest, I always used…
To be honest, I always used the phrase Timechain as a synonym for Blockchain.
Nevertheless, the Blockchain is probably more commonly used as the description for a decentralized digital ledger that records all transactions on a network and the timechain is a specific aspect of the blockchain, that refers to the chronological order of blocks in the blockchain.
By the why, Satoshi Nakamoto said proof-of-work chain and used other descriptions around the concept of a digital chain, but seems to have not used the word Blockchain, at least not in his whitepaper:
