Source : Webster's Revised Unabridged Dictionary (1913)

Particle \Par"ti*cle\, n. [L. particula, dim of pars, gen
   partis, a part: cf. F. particule. See {Part}, and cf.
   {Parcel}.]
   1. A minute part or portion of matter; a morsel; a little
      bit; an atom; a jot; as, a particle of sand, of wood, of
      dust.

            The small size of atoms which unite To make the
            smallest particle of light.           --Blackmore.

   2. Any very small portion or part; the smallest portion; as,
      he has not a particle of patriotism or virtue.

            The houses had not given their commissioners
            authority in the least particle to recede.
                                                  --Clarendon.

   3. (R. C. Ch.)
      (a) A crumb or little piece of concecrated host.
      (b) The smaller hosts distributed in the communion of the
          laity. --Bp. Fitzpatrick.

   4. (Gram.) A subordinate word that is never inflected (a
      preposition, conjunction, interjection); or a word that
      can not be used except in compositions; as, ward in
      backward, ly in lovely.

Source : WordNet®

particle
     n 1: (nontechnical usage) a tiny piece of anything [syn: {atom},
          {molecule}, {corpuscle}, {mote}, {speck}]
     2: a body having finite mass and internal structure but
        negligible dimensions
     3: a function word that can be used in English to form phrasal
        verbs