Satoshi himself coined the term timechain on the bitcoin talk forums, discussing and explaining his bitcoin idea before the release of the bitcoin whitepaper. It was part of the pre-release source code of Bitcoin!
The word Timechain is used by Satoshi to refer to the nature of the Bitcoin chain of timestamped events in history.
Timechain not Blockchain!
The timechain is a tree shaped structure starting with the genesis block at the root with each block having multiple candidates to be the next block. pprev and pnext link a path through the main longest chain. pnext will only point forward to the longest branch, or will be null if the block is not part of the longest chain
Satoshi Nakamoto