ADJECTIVE (3)

1. lacking in interest or care or feeling;
- Example: "the average American...is unconcerned that his or her plight is the result of a complex of personal and economic and governmental actions...beyond the normal citizen's comprehension and control"
- Example: "blithely unconcerned about his friend's plight"

2. easy in mind; not worried;
- Example: "the prisoner seems entirely unconcerned as to the outcome of the examination"

3. not occupied or engaged with;
- Example: "readers unconcerned with style"

The Collaborative International Dictionary of English v.0.48:

Unconcerned \Un`con*cerned"\, a.
   Not concerned; not anxious or solicitous; easy in mind;
   carelessly secure; indifferent; as, to be unconcerned at what
   has happened; to be unconcerned about the future. --
   Un`con*cern"ed*ly, adv. -- Un`con*cern"ed*ness, n.
   [1913 Webster]

         Happy mortals, unconcerned for more.     --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unconcerned
    adj 1: lacking in interest or care or feeling; "the average
           American...is unconcerned that his or her plight is the
           result of a complex of personal and economic and
           governmental actions...beyond the normal citizen's
           comprehension and control"; "blithely unconcerned about
           his friend's plight" [ant: concerned]
    2: easy in mind; not worried; "the prisoner seems entirely
       unconcerned as to the outcome of the examination"
    3: not occupied or engaged with; "readers unconcerned with
       style"

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "unconcerned":
   Laodicean, Olympian, aloof, apathetic, ataractic, benumbed, blah,
   blase, bored, careless, casual, collected, comatose, composed,
   cool, degage, desensitized, detached, devil-may-care,
   disinterested, dispassionate, disregardful, distant, dull, easy,
   easygoing, free and easy, heartless, hebetudinous, heedless,
   hopeless, impassive, in a stupor, inattentive, incurious,
   indifferent, inexcitable, insouciant, lackadaisical, languid,
   lethargic, listless, mindless, negligent, nonchalant, numb, numbed,
   offhand, passive, perfunctory, phlegmatic, pluckless, pococurante,
   reckless, regardless, remote, resigned, slack, sluggish, soporific,
   spiritless, spunkless, stoic, stolid, stupefied, supine, torpid,
   turned-off, unanxious, uncaring, undiscriminating, uninquiring,
   uninterested, uninvolved, unmindful, unsolicitous, withdrawn