The Collaborative International Dictionary of English v.0.48:

Accumulator \Ac*cu"mu*la`tor\, n. [L.]
   1. One who, or that which, accumulates, collects, or amasses.
      [1913 Webster]

   2. (Mech.) An apparatus by means of which energy or power can
      be stored, such as the cylinder or tank for storing water
      for hydraulic elevators, the secondary or storage battery
      used for accumulating the energy of electrical charges,
      etc.
      [1913 Webster]

   3. A system of elastic springs for relieving the strain upon
      a rope, as in deep-sea dredging.
      [1913 Webster]

WordNet (r) 3.0 (2006):

accumulator
    n 1: a person who is employed to collect payments (as for rent
         or taxes) [syn: collector, gatherer, accumulator]
    2: a voltaic battery that stores electric charge [syn: storage
       battery, accumulator]
    3: (computer science) a register that has a built-in adder that
       adds an input number to the contents of the register [syn:
       accumulator, accumulator register]

The Jargon File (version 4.4.7, 29 Dec 2003):

accumulator
 n. obs.

    1. Archaic term for a register. On-line use of it as a synonym for register
    is a fairly reliable indication that the user has been around for quite a
    while and/or that the architecture under discussion is quite old. The term
    in full is almost never used of microprocessor registers, for example,
    though symbolic names for arithmetic registers beginning in ?A? derive from
    historical use of the term accumulator (and not, actually, from
    ?arithmetic?). Confusingly, though, an ?A? register name prefix may also
    stand for address, as for example on the Motorola 680x0 family.

    2. A register being used for arithmetic or logic (as opposed to addressing
    or a loop index), especially one being used to accumulate a sum or count of
    many items. This use is in context of a particular routine or stretch of
    code. ?The FOOBAZ routine uses A3 as an accumulator.?

    3. One's in-basket (esp. among old-timers who might use sense 1). ?You want
    this reviewed? Sure, just put it in the accumulator.? (See stack.)


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

accumulator

    In a central processing unit, a register in
   which intermediate results are stored.  Without an
   accumulator, it would be necessary to write the result of each
   calculation (addition, multiplication, shift, etc.) to main
   memory and read them back.  Access to main memory is slower
   than access to the accumulator which usually has direct paths
   to and from the arithmetic and logic unit (ALU).

   The canonical example is summing a list of numbers.  The
   accumulator is set to zero initially, each number in turn is
   added to the value in the accumulator and only when all
   numbers have been added is the result written to main memory.

   Modern CPUs usually have many registers, all or many of which
   can be used as accumulators.  For this reason, the term
   "accumulator" is somewhat archaic.  Use of it as a synonym for
   "register" is a fairly reliable indication that the user has
   been around for quite a while and/or that the architecture
   under discussion is quite old.  The term in full is almost
   never used of microprocessor registers, for example, though
   symbolic names for arithmetic registers beginning in "A"
   derive from historical use of the term "accumulator" (and not,
   actually, from "arithmetic").  Confusingly, though, an "A"
   register name prefix may also stand for "address", as for
   example on the Motorola 680x0 family.

   2.  A register, memory location or variable being
   used for arithmetic or logic (as opposed to addressing or a
   loop index), especially one being used to accumulate a sum or
   count of many items.  This use is in context of a particular
   routine or stretch of code.  "The FOOBAZ routine uses A3 as an
   accumulator."

   [Jargon File]

   (1999-04-20)