The Collaborative International Dictionary of English v.0.48:

Impersonal \Im*per"son*al\, a. [L. impersonalis; pref. im- not +
   personalis personal: cf. F. impersonnel. See Personal.]
   Not personal; not representing a person; not having
   personality.
   [1913 Webster]

         An almighty but impersonal power, called Fate. --Sir J.
                                                  Stephen.
   [1913 Webster]

   Impersonal verb (Gram.), a verb used with an indeterminate
      subject, commonly, in English, with the impersonal pronoun
      it; as, it rains; it snows; methinks (it seems to me).
      Many verbs which are not strictly impersonal are often
      used impersonally; as, it goes well with him.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Impersonal \Im*per"son*al\, n.
   That which wants personality; specifically (Gram.), an
   impersonal verb.
   [1913 Webster]

WordNet (r) 3.0 (2006):

impersonal
    adj 1: not relating to or responsive to individual persons; "an
           impersonal corporation"; "an impersonal remark" [ant:
           personal]
    2: having no personal preference; "impersonal criticism"; "a
       neutral observer" [syn: impersonal, neutral]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "impersonal":
   Olympian, abstract, aloof, backward, bashful, blank, candid,
   chilled, chilly, cold, cold-blooded, colorless, constrained,
   conventionalized, cool, detached, discreet, disinterested,
   dispassionate, distant, emotionless, equal, equitable, evenhanded,
   expressionless, external, extraneous, extraorganismal, extrinsic,
   fair, forbidding, foreign, formal, formalist, formalistic,
   formulary, frigid, frosty, guarded, icy, impartial, impassive,
   inaccessible, indifferent, introverted, just, legalistic, lofty,
   matter-of-fact, mechanical, modest, neutral, nominal,
   nonsubjective, objective, offish, outlying, outside, outward,
   pedantic, poker-faced, prim, remote, removed, repressed, reserved,
   restrained, reticent, retiring, rigid, selfless, shrinking,
   standoff, standoffish, stiff, strait-laced, stuffy, stylized,
   subdued, superficial, suppressed, surface, unaffable,
   unapproachable, unbiased, uncolored, uncongenial, undazzled,
   undemonstrative, unexpansive, unfriendly, ungenial, unimpassioned,
   uninfluenced, unjaundiced, unprejudiced, unprepossessed, unselfish,
   unswayed, withdrawn, wooden