Synchronous

1. At the same time, at the same frequency.

Synonyms: simultaneous, in phase, in synch, in step

Antonyms: asynchronous, antisynchronous

2. (computing, of communication) Single-threaded; blocking; occurring in the same thread as other computations, thereby preventing those computations from resuming until the communication is complete.

Synonyms: blocking, modal, single-threaded

Antonym: asynchronous