The Collaborative International Dictionary of English v.0.48:

Fluster \Flus"ter\, v. t. [imp. & p. p. Flustered; p. pr. &
   vb. n. Flustering.] [Cf. Icel. flaustra to be flustered,
   flaustr a fluster.]
   To make hot and rosy, as with drinking; to heat; hence, to
   throw into agitation and confusion; to confuse; to muddle.
   [1913 Webster]

         His habit or flustering himself daily with claret.
                                                  --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flustered
    adj 1: thrown into a state of agitated confusion; (`rattled' is
           an informal term) [syn: flustered, hot and
           bothered(p), perturbed, rattled]