adjective (a)

• occurring or existing at the same time or having the same period or phase(adj.all)

  Example:
  Recovery was synchronous with therapy.
  A synchronous set of clocks.
  The synchronous action of a bird's wings in flight.
  Synchronous oscillations.
  

  Synonym:
  synchronal, synchronic
  Antonym:
  asynchronous
  

  source: wordnet30
• (digital communication) pertaining to a transmission technique that requires a common clock signal (a timing reference) between the communicating devices in order to coordinate their transmissions(adj.all)

  source: wordnet30
• Happening at the same time; simultaneous.(adjective)

  source: webster1913