Source : Webster's Revised Unabridged Dictionary (1913)

Indivisible \In`di*vis"i*ble\, a. [L. indivisibilis: cf. F.
   indivisible. See {In-} not, and {Divisible}.]
   1. Not divisible; incapable of being divided, separated, or
      broken; not separable into parts. ``One indivisible point
      of time.'' --Dryden.

   2. (Math.) Not capable of exact division, as one quantity by
      another; incommensurable.

Indivisible \In`di*vis"i*ble\, n.
   1. That which is indivisible.

            By atom, nobody will imagine we intend to express a
            perfect indivisible, but only the least sort of
            natural bodies.                       --Digby.

   2. (Geom.) An infinitely small quantity which is assumed to
      admit of no further division.

   {Method of indivisibles}, a kind of calculus, formerly in
      use, in which lines were considered as made up of an
      infinite number of points; surfaces, as made up of an
      infinite number of lines; and volumes, as made up of an
      infinite number of surfaces.

Source : WordNet®

indivisible
     adj : impossible of undergoing division; "an indivisible union of
           states"; "one nation indivisible" [ant: {divisible}]