The Collaborative International Dictionary of English v.0.48:

Redundance \Re*dun"dance\ (r?*d?n"dans), Redundancy
\Re*dun"dan*cy\ (-dan*s?), n. [L. redundantia: cf. F.
   redondance.]
   [1913 Webster]
   1. The quality or state of being redundant; superfluity;
      superabundance; excess.
      [1913 Webster]

   2. That which is redundant or in excess; anything superfluous
      or superabundant.
      [1913 Webster]

            Labor . . . throws off redundacies.   --Addison.
      [1913 Webster]

   3. (Law) Surplusage inserted in a pleading which may be
      rejected by the court without impairing the validity of
      what remains.
      [1913 Webster]

WordNet (r) 3.0 (2006):

redundancy
    n 1: repetition of messages to reduce the probability of errors
         in transmission
    2: the attribute of being superfluous and unneeded; "the use of
       industrial robots created redundancy among workers" [syn:
       redundancy, redundance]
    3: (electronics) a system design that duplicates components to
       provide alternatives in case one component fails
    4: repetition of an act needlessly

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "redundancy":
   EDP, abundance, amplitude, avalanche, battology, bedizenment, bit,
   channel, circumambages, circumbendibus, circumlocution,
   cloud of words, communication explosion, communication theory,
   copiousness, data retrieval, data storage, decoding, deluge,
   diffuseness, diffusion, diffusiveness, duplication,
   duplication of effort, effusion, effusiveness,
   electronic data processing, embarras de richesses, embellishment,
   encoding, enough, entropy, excess, expletive, extravagance,
   extravagancy, exuberance, fat, featherbedding, fecundity,
   fertility, filling, flatulence, flood, fluency, formlessness,
   frill, frills, frippery, gingerbread, gush, gushing, inflatedness,
   inflation, information explosion, information theory, inundation,
   landslide, lavishness, logorrhea, luxury, macrology, money to burn,
   more than enough, needlessness, noise, ornamentation, outpour,
   overabundance, overaccumulation, overadornment, overage,
   overbounteousness, overcopiousness, overdose, overflow, overlap,
   overlavishness, overluxuriance, overmeasure, overmuchness,
   overnumerousness, overplentifulness, overplenty, overplus,
   overpopulation, overprofusion, oversufficiency, oversupply,
   padding, palilogy, payroll padding, periphrase, periphrasis,
   plenty, pleonasm, plethora, prodigality, productivity, profuseness,
   profusion, prolificacy, prolificity, prolixity, rampancy, rankness,
   redundance, reiteration, reiterativeness, repetition for effect,
   repetitiveness, roundabout, signal, spate, stammering, stuttering,
   superabundance, superfluity, superfluousness, superflux, surplus,
   surplusage, talkativeness, tautologism, tautology, teemingness,
   tirade, tumidity, turgidity, unnecessariness, verbality,
   verbosity



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

redundancy

   1.  The provision of multiple
   interchangeable components to perform a single function in
   order to provide resilience (to cope with failures and
   errors).  Redundancy normally applies primarily to hardware.
   For example, a cluster may contain two or three computers
   doing the same job.  They could all be active all the time
   thus giving extra performance through parallel processing
   and load balancing; one could be active and the others
   simply monitoring its activity so as to be ready to take over
   if it failed ("warm standby"); the "spares" could be kept
   turned off and only switched on when needed ("cold standby").
   Another common form of hardware redundancy is disk
   mirroring.

   2.  data redundancy.

   (1995-05-09)


Bouvier's Law Dictionary, Revised 6th Ed (1856):

REDUNDANCY. Matter introduced in an answer, or pleading, which is foreign to
the bill or articles.
     2. In the case of Dysart v. Dysart, 3 Curt. Ecc. R. 543, in giving the
judgment of the court, Dr. Lushington says: "It may not, perhaps, be easy to
define the meaning of this term [redundant] in a short sentence, but the
true meaning I take to be this: the respondent is not to insert in his
answer any matter foreign to the articles he is called upon to answer,
although such matter may be admissible in a plea; but he may, in his answer,
plead matter by way of explanation pertinent to the articles, even if such
matter shall be solely in his own knowledge and to such extent incapable of
proof; or he may state matter which can be substantiated by witnesses; but
in this latter instance, if such matter be introduced into the answer and
not afterwards put in the plea or proved, the court will give no weight or
credence to such part of the answer."
     3. A material distinction is to be observed between redundancy in the
allegation and redundancy in the proof. In the former case, a variance
between the allegation and the proof will be fatal if the redundant
allegations are descriptive of that which is essential. But in the latter
case, redundancy cannot vitiate, because more is proved than is alleged,
unless the matter superfluously proved goes to contradict some essential
part of the allegation. 1 Greenl. Ev. Sec. 67; 1 Stark. Ev. 401.