synchronous describes things happening, existing, or arising at precisely the same time — coordinated to a shared clock, so that each party's participation depends on the others being present.
Synchronous communication is the kind that has to be attended. A phone call, a video conference, a meeting, a live class: the connection exists only while everyone holds it open, and anyone outside that window misses it entirely. The demand is real, since all parties must be available at once, and so is the return, since a misunderstanding surfaces and resolves inside the same minute rather than across a day of replies.
In computing the word describes operations bound to a common timing signal, or a call that blocks until it returns a result. A synchronous request holds the caller in place — nothing else proceeds until the answer arrives. The trade is the same one the human sense makes: coordination overhead bought in exchange for immediacy and simpler ordering.
The word comes through Late Latin from the Greek syn-, "together," and chronos, "time." Its counterpart, 📝asynchronous, is not merely its absence: synchronous work spends availability to buy immediacy, and asynchronous work spends immediacy to buy availability.