The Collaborative International Dictionary of English v.0.48:

Extra- \Ex"tra-\ [L., fr. exter. See Exterior.]
   A Latin preposition, denoting beyond, outside of; -- often
   used in composition as a prefix signifying outside of,
   beyond, besides, or in addition to what is denoted by the
   word to which it is prefixed.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Extra \Ex"tra\, a.
   Beyond what is due, usual, expected, or necessary;
   additional; supernumerary; also, extraordinarily good;
   superior; as, extra work; extra pay. "By working extra
   hours." --H. Spencer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Extra \Ex"tra\, n.; pl. Extras.
   1. Something in addition to what is due, expected, or
      customary; esp., an added charge or fee, or something for
      which an additional charge is made; as, at some hotels air
      conditioning is an extra.
      [Webster 1913 Suppl.]

   2. An edition of a newspaper issued at a time other than the
      regular one.
      [Webster 1913 Suppl.]

   3. (Cricket) A run, as from a bye, credited to the general
      score but not made from a hit.
      [Webster 1913 Suppl.]

   4. Something of an extra quality or grade.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

extra
    adv 1: unusually or exceptionally; "an extra fast car"
    adj 1: more than is needed, desired, or required; "trying to
           lose excess weight"; "found some extra change lying on
           the dresser"; "yet another book on heraldry might be
           thought redundant"; "skills made redundant by
           technological advance"; "sleeping in the spare room";
           "supernumerary ornamentation"; "it was supererogatory of
           her to gloat"; "delete superfluous (or unnecessary)
           words"; "extra ribs as well as other supernumerary
           internal parts"; "surplus cheese distributed to the
           needy" [syn: excess, extra, redundant, spare,
           supererogatory, superfluous, supernumerary,
           surplus]
    2: added to a regular schedule; "a special holiday flight"; "put
       on special buses for the big game" [syn: extra, special]
    3: further or added; "called for additional troops"; "need extra
       help"; "an extra pair of shoes" [syn: extra, additional]
    n 1: a minor actor in crowd scenes [syn: supernumerary, spear
         carrier, extra]
    2: an additional edition of a newspaper (usually to report a
       crisis)
    3: something additional of the same kind; "he always carried
       extras in case of an emergency" [syn: extra, duplicate]

Moby Thesaurus II by Grady Ward, 1.0:

213 Moby Thesaurus words for "extra":
   above, accessory, accident, accidental, added, addendum, addition,
   additional, additionally, adjunct, adscititious, adventitious,
   again, all included, also, altogether, amazingly,
   among other things, ancillary, and all, and also, and so, another,
   appendage, appurtenance, appurtenant, as a bonus, as well,
   ascititious, au reste, auxiliary, balance, beside, besides, beyond,
   bit player, bonus, casual, circumstantial, collateral,
   considerably, contingency, contingent, contributory, daily,
   daily newspaper, de trop, decoration, dividend, else, en plus,
   especially, exceptionally, excess, extra added attraction,
   extra dash, extra edition, extraordinarily, extremely, farther,
   figurant, figurante, filigree, filling, fillip, flourish,
   for lagniappe, fortuitous, fresh, frill, further, furthermore,
   gazette, gratuity, happenstance, held back, held in reserve,
   held out, in abeyance, in addition, in hand, incidental,
   inessential, inter alia, into the bargain, item, kicker, lagniappe,
   leftover, likewise, margin, markedly, mere chance, mint, more,
   moreover, mute, national newspaper, neighborhood newspaper, new,
   news, newspaper, newspaper of record, nonessential, not-self,
   notably, noticeably, occasional, odd, off, on the side, on top of,
   original, ornament, other, out-of-the-way, over, over and above,
   overage, overmeasure, overplus, overrun, overset, overstock,
   oversupply, padding, paper, part-time, particularly, plus,
   pourboire, premium, pristine, put aside, put by, rag, rarely,
   remainder, remaining, remarkably, reserve, saved, secondary, sheet,
   side, similarly, something extra, spare, spear-carrier, special,
   special edition, stand-in, standby, stored, strikingly, stuffing,
   subsidiary, substitute, supe, super, superadded, superaddition,
   superfluous, supernumerary, supervenient, supplement, supplemental,
   supplementary, support, supporting actor, supporting cast,
   surcharge, surplus, surplusage, surprisingly, suspended, tabloid,
   then, therewith, tip, to boot, to spare, too, trimming, twist,
   ulterior, unapplied, unbeaten, uncommon, uncommonly, unconsumed,
   understudy, unemployed, unessential, unexercised, unexpectedly,
   unexpended, unhandled, unspent, untapped, untouched, untrodden,
   unused, unusually, unutilized, very, waived, walk-on,
   walking gentleman, weekly, weekly newspaper, wrinkle, yet



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

EXTRA
       EXecutionTRace Analyser (IBM, OS/2)


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

EXTRA

   Object-oriented, Pascal style, handles sets.  "A Data Model
   and Query Language for EXODUS", M.J. Carey et al, SIGMOD 88
   Conf Proc, pp.413- 423, ACM SIGMOD Record 17:3 (Sept 1988).