ADJECTIVE (2)

1. (digital communication) pertaining to a transmission technique that does not require a common clock between the communicating devices; timing signals are derived from special characters in the data stream itself;

2. not synchronous; not occurring or existing at the same time or having the same period or phase;

The Collaborative International Dictionary of English v.0.48:

Asynchronous \A*syn"chro*nous\, a. [Gr. ? not + synchronous.]
   Not simultaneous; not concurrent in time; -- opposed to
   synchronous.

   Syn: nonsynchronous, unsynchronized, unsynchronous.
        [Webster 1913 Suppl.]

   2. (Paleontology) occurring in different geologic times; --
      of taxa/ synchronous

   Syn: allochronic
        [WordNet 1.5 +PJC]

   3. chronologically misplaced; belonging to a different time
      or era

   Syn: anachronic, anachronous, anachronistic
        [WordNet 1.5 +PJC]

   4. (Computers) occurring at different speeds in different
      computers connected by a data transmission link; -- said
      of methods data of transmission between computers.
      Opposite of synchronous.
      [PJC]

WordNet (r) 3.0 (2006):

asynchronous
    adj 1: (digital communication) pertaining to a transmission
           technique that does not require a common clock between
           the communicating devices; timing signals are derived
           from special characters in the data stream itself [ant:
           synchronous]
    2: not synchronous; not occurring or existing at the same time
       or having the same period or phase [ant: synchronal,
       synchronic, synchronous]

The Free On-line Dictionary of Computing (30 December 2018):

asynchronous

    Not synchronised by a shared signal such as
   clock or semaphore, proceeding independently.

   Opposite: synchronous.

   1.  A process in a multitasking system
   whose execution can proceed independently, "in the
   background".  Other processes may be started before the
   asynchronous process has finished.

   2.  A communications system in which data
   transmission may start at any time and is indicated by a
   start bit, e.g. EIA-232.  A data byte (or other element
   defined by the protocol) ends with a stop bit.  A
   continuous marking condition (identical to stop bits but not
   quantized in time), is then maintained until data resumes.

   (1995-12-08)