The Collaborative International Dictionary of English v.0.48:

Unco \Un"co\, a. [Scot. The same word as E. uncouth.]
   Unknown; strange, or foreign; unusual, or surprising; distant
   in manner; reserved. [Scot.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Unco \Un"co\, adv.
   In a high degree; to a great extent; greatly; very. [Prov.
   Eng. & Scot.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Unco \Un"co\, n.
   A strange thing or person. [Scot.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

unco
    adv 1: to a remarkable degree or extent; "she was unusually
           tall" [syn: unusually, remarkably, outstandingly,
           unco] [ant: commonly, normally, ordinarily,
           unremarkably, usually]