The Collaborative International Dictionary of English v.0.48:

Plus \Plus\, a. [L., more; akin to Gr. ?, ?, and E. full. See
   Full, a., and cf. Pi[`u], Pleonasm.]
   [1913 Webster]
   1. (Math.) More, required to be added; positive, as
      distinguished from negative; -- opposed to minus.
      [1913 Webster]

   2. Hence, in a literary sense, additional; real; actual.
      [1913 Webster]

            Success goes invariably with a certain plus or
            positive power.                       --Emerson.
      [1913 Webster]

   Plus sign (Math.), the sign (+) which denotes addition, or
      a positive quantity.
      [1913 Webster]

WordNet (r) 3.0 (2006):

plus
    adj 1: on the positive side or higher end of a scale; "a plus
           value"; "temperature of plus 5 degrees"; "a grade of C
           plus" [ant: minus]
    2: involving advantage or good; "a plus (or positive) factor"
       [syn: plus, positive]
    n 1: a useful or valuable quality [syn: asset, plus] [ant:
         liability]
    2: the arithmetic operation of summing; calculating the sum of
       two or more numbers; "the summation of four and three gives
       seven"; "four plus three equals seven" [syn: summation,
       addition, plus]

Moby Thesaurus II by Grady Ward, 1.0:

146 Moby Thesaurus words for "plus":
   above, accessory, add, added, added to, addend, addition,
   additional, additionally, adjoin, advantage, affix, again,
   agglutinate, aggrandize, all included, along with, also,
   altogether, among other things, ancillary, and, and all, and also,
   and so, annex, another, append, as well, as well as, asset, attach,
   attended by, au reste, augment, auxiliary, balance, beef up,
   benefit, beside, besides, beyond, bonus, boost, build, burden,
   collateral, complicate, compound, conjoin, contributory,
   coupled with, decorate, dividend, else, en plus, encumber, enlarge,
   expand, extra, farther, for lagniappe, fresh, further, furthermore,
   gain, glue on, gratuity, hitch on, in addition, in addition to,
   in conjunction with, including, inclusive of, infix, inter alia,
   into the bargain, item, join with, lagniappe, leftover, let alone,
   likewise, linked to, magnify, margin, minus, more, moreover,
   negative, new, not to mention, on the side, on top of, ornament,
   other, over, over and above, overage, overmeasure, overplus,
   overrun, overset, overstock, oversupply, paste on, plus sign,
   positive, postfix, pourboire, prefix, profit, put with, remainder,
   return, saddle with, similarly, slap on, something extra, spare,
   subjoin, subtotal, suffix, sum, summation, superadd, supernumerary,
   superpose, supplemental, supplementary, surplus, surplusage,
   tack on, tag, tag on, then, therewith, tip, to boot, together with,
   too, total, ulterior, unite with, with, yet



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

PLUS

   Late 60's.  Machine-oriented systems language used internally
   by Univac.


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

plus
+

    "+", ASCII character 43, 0x2B.  The mathematical
   symbol for the addition operator, also used with the same
   meaning in arithmetic expressions in nearly all programming
   languages.

   Common names: ITU-T: plus; add.  Rare: cross; INTERCAL:
   intersection.

   In programming, the operator is sometimes overloaded to
   perform other tasks like concatenating strings.  In the C
   language and its many imitators, the symbol is doubled, as in
   "x++" or "++x" to give an increment operator that adds one to
   its operand ("x" in this case) and also returns x's previous
   or resulting value respectively.

   In a regular expression, "+" means match one or more
   instances of the previous pattern.  Thus /b(an)+a/ would match
   any of "bana", "banana", "bananana", etc. (see banana
   problem).

   (2010-03-20)