The Collaborative International Dictionary of English v.0.48:

Register \Reg"is*ter\ (r?j"?s*t?r), n. [OE. registre, F.
   registre, LL. registrum,regestum, L. regesta, pl., fr.
   regerere, regestum, to carry back, to register; pref. re- re-
   + gerere to carry. See Jest, and cf. Regest.]
   1. A written account or entry; an official or formal
      enumeration, description, or record; a memorial record; a
      list or roll; a schedule.
      [1913 Webster]

            As you have one eye upon my follies, . . . turn
            another into the register of your own. --Shak.
      [1913 Webster]

   2. (Com.)
      (a) A record containing a list and description of the
          merchant vessels belonging to a port or customs
          district.
      (b) A certificate issued by the collector of customs of a
          port or district to the owner of a vessel, containing
          the description of a vessel, its name, ownership, and
          other material facts. It is kept on board the vessel,
          to be used as an evidence of nationality or as a
          muniment of title.
          [1913 Webster]

   3. [Cf. LL. registrarius. Cf. Regisrar.] One who registers
      or records; a registrar; a recorder; especially, a public
      officer charged with the duty of recording certain
      transactions or events; as, a register of deeds.
      [1913 Webster]

   4. That which registers or records. Specifically:
      (a) (Mech.) A contrivance for automatically noting the
          performance of a machine or the rapidity of a process.
      (b) (Teleg.) The part of a telegraphic apparatus which
          records automatically the message received.
      (c) A machine for registering automatically the number of
          persons passing through a gateway, fares taken, etc.;
          a telltale.
          [1913 Webster]

   5. A lid, stopper, or sliding plate, in a furnace, stove,
      etc., for regulating the admission of air to the fuel;
      also, an arrangement containing dampers or shutters, as in
      the floor or wall of a room or passage, or in a chimney,
      for admitting or excluding heated air, or for regulating
      ventilation.
      [1913 Webster]

   6. (Print.)
      (a) The inner part of the mold in which types are cast.
      (b) The correspondence of pages, columns, or lines on the
          opposite or reverse sides of the sheet.
      (c) The correspondence or adjustment of the several
          impressions in a design which is printed in parts, as
          in chromolithographic printing, or in the manufacture
          of paper hangings. See Register, v. i. 2.
          [1913 Webster]

   7. (Mus.)
      (a) The compass of a voice or instrument; a specified
          portion of the compass of a voice, or a series of
          vocal tones of a given compass; as, the upper, middle,
          or lower register; the soprano register; the tenor
          register.
          [1913 Webster]

   Note: In respect to the vocal tones, the thick register
         properly extends below from the F on the lower space of
         the treble staff. The thin register extends an octave
         above this. The small register is above the thin. The
         voice in the thick register is called the chest voice;
         in the thin, the head voice. Falsetto is a kind off
         voice, of a thin, shrull quality, made by using the
         mechanism of the upper thin register for tones below
         the proper limit on the scale. --E. Behnke.
         [1913 Webster]
      (b) A stop or set of pipes in an organ.
          [1913 Webster]

   Parish register, A book in which are recorded the births,
      baptisms, marriages, deaths, and burials in a parish.
      [1913 Webster]

   Syn: List; catalogue; roll; record; archives; chronicle;
        annals. See List.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Register \Reg"is*ter\ (r[e^]j"[i^]s*t[~e]r), v. t. [imp. & p. p.
   Registere (-t?rd); p. pr. & vb. n. Registering.] [Cf. F.
   regisrer, exregistrer, LL. registrare. See Register, n.]
   1. To enter in a register; to record formally and distinctly,
      as for future use or service.
      [1913 Webster]

   2. To enroll; to enter in a list.
      [1913 Webster]

            Such follow him as shall be registered. --Milton.
      [1913 Webster]

   3. (Securities) To enter the name of the owner of (a share of
      stock, a bond, or other security) in a register, or record
      book. A registered security is transferable only on the
      written assignment of the owner of record and on surrender
      of his bond, stock certificate, or the like.
      [Webster 1913 Suppl.]

   Registered letter, a letter, the address of which is, on
      payment of a special fee, registered in the post office
      and the transmission and delivery of which are attended to
      with particular care.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Register \Reg"is*ter\, v. i.
   1. To enroll one's name in a register.
      [1913 Webster]

   2. (Print.) To correspond in relative position; as, two
      pages, columns, etc., register when the corresponding
      parts fall in the same line, or when line falls exactly
      upon line in reverse pages, or (as in chromatic printing)
      where the various colors of the design are printed
      consecutively, and perfect adjustment of parts is
      necessary.
      [1913 Webster]

WordNet (r) 3.0 (2006):

register
    n 1: an official written record of names or events or
         transactions [syn: register, registry]
    2: (music) the timbre that is characteristic of a certain range
       and manner of production of the human voice or of different
       pipe organ stops or of different musical instruments
    3: a book in which names and transactions are listed
    4: (computer science) memory device that is the part of computer
       memory that has a specific address and that is used to hold
       information of a specific kind
    5: an air passage (usually in the floor or a wall of a room) for
       admitting or excluding heated air from the room
    6: a regulator (as a sliding plate) for regulating the flow of
       air into a furnace or other heating device
    7: a cashbox with an adding machine to register transactions;
       used in shops to add up the bill [syn: cash register,
       register]
    v 1: record in writing; enter into a book of names or events or
         transactions
    2: record in a public office or in a court of law; "file for
       divorce"; "file a complaint" [syn: file, register]
    3: enroll to vote; "register for an election"
    4: be aware of; "Did you register any change when I pressed the
       button?" [syn: record, register]
    5: indicate a certain reading; of gauges and instruments; "The
       thermometer showed thirteen degrees below zero"; "The gauge
       read `empty'" [syn: read, register, show, record]
    6: have one's name listed as a candidate for several parties
       [syn: cross-file, register]
    7: show in one's face; "Her surprise did not register"
    8: manipulate the registers of an organ
    9: send by registered mail; "I'd like to register this letter"
    10: enter into someone's consciousness; "Did this event register
        in your parents' minds?"

The Free On-line Dictionary of Computing (19 January 2023):

register

   1. One of a small number of high-speed memory locations in a
   computer's CPU.  Registers differ from ordinary
   random-access memory in several respects:

   There are only a small number of registers (the "register
   set"), typically 32 in a modern processor though some,
   e.g. SPARC, have as many as 144.  A register may be directly
   addressed with a few bits.  In contrast, there are usually
   millions of words of main memory (RAM), requiring at least
   twenty bits to specify a memory location.  Main memory
   locations are often specified indirectly, using an indirect
   addressing mode where the actual memory address is held in a
   register.

   Registers are fast; typically, two registers can be read and a
   third written -- all in a single cycle.  Memory is slower; a
   single access can require several cycles.

   The limited size and high speed of the register set makes it
   one of the critical resources in most computer architectures.
   Register allocation, typically one phase of the back-end,
   controls the use of registers by a compiled program.

   See also accumulator, FUBAR, orthogonal, register
   dancing, register allocation, register spilling.

   2. An addressable location in a memory-mapped peripheral
   device.  E.g. the transmit data register in a UART.