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