adj.

1. Occurring or existing at the same time. See synonyms at contemporary.
2. Moving or operating at the same rate.
3. 1. Having identical periods.
   2. Having identical period and phase.

[From Late Latin synchronus, from Greek sunkhronos : sun-, syn- + khronos, time.]

synchronously syn'chro·nous·ly adv.
synchronousness syn'chro·nous·ness n.

adjective

Belonging to the same period of time as another: coetaneous, coeval, coexistent, concurrent, contemporaneous, contemporary, synchronic. See time.

adj

Having constant time intervals between events or occurrences.

Occurring at the same time.

• s. diaphragmatic flutter — see synchronous diaphragmatic flutter.
• s. timer — an oldfashioned timer on an x-ray machine that permits of very short exposure times but has to be reset after each exposure. Use of this kind of timer is no longer legal in most countries.

Two or more signals in step or in phase.

IN BRIEF: Happening, existing, or arising at precisely the same time.

It almost alarms me how free I feel on the ice....It’s exciting when your whole body is moving in synchronous motion. — Tenley Albright, U.S. ice skater and physician.