\Un*prob"a*bly\, adv. [Pref. un- not + probably.]
Improbably.

\Un*prob"a*bly\, adv. [Un- + L. probabilis
approvable, fr. probare to approve. Cf. {Probable}.]
In a manner not to be approved of; improperly. [Obs. & R.]
      To diminish, by the authority of wise and knowing men,
      things unjustly and unprobably crept in. --Strype.