The Collaborative International Dictionary of English v.0.48:

Expletive \Ex"ple*tive\, n.
   A word, letter, or syllable not necessary to the sense, but
   inserted to fill a vacancy; an oath.
   [1913 Webster]

         While explectives their feeble aid to join,
         And ten low words oft creep in one dull line. --Pope.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Expletive \Ex"ple*tive\, a. [L. expletivus, from expletus, p. p.
   of explere to fill up; ex out+plere to fill, akin to plenus
   full: cf. F. expl['e]tif. See Full.]
   Filling up; hence, added merely for the purpose of filling
   up; superfluous. "Expletive imagery." --Hallam.
   [1913 Webster]

         Expletive phrases to plump his speech.   --Barrow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

expletive
    n 1: profane or obscene expression usually of surprise or anger;
         "expletives were deleted" [syn: curse, curse word,
         expletive, oath, swearing, swearword, cuss]
    2: a word or phrase conveying no independent meaning but added
       to fill out a sentence or metrical line

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "expletive":
   battology, bedizenment, blurt, curse, cuss, cuss word, de trop,
   dirty name, dirty word, dispensable, duplication,
   duplication of effort, dysphemism, ecphonesis, ejaculation,
   embellishment, epithet, excess, exclamation, expendable,
   extravagance, fat, featherbedding, filler, filling, foul invective,
   frill, frills, frippery, gingerbread, gratuitous, in excess,
   iterative, luxury, macrology, naughty word, needless, needlessness,
   no-no, nonessential, oath, obscenity, ornamentation, outburst,
   overadornment, overlap, padding, payroll padding, pleonasm,
   pleonastic, profane oath, prolix, prolixity, redundance,
   redundancy, redundant, reiterative, repetitious, spare, stammering,
   stuttering, supererogatory, superfluity, superfluous,
   superfluousness, swear, swearword, tautologic, tautological,
   tautologism, tautologous, tautology, to spare, uncalled-for,
   unessential, unnecessariness, unnecessary, unneeded, verbose,
   verbosity, wordy