The Collaborative International Dictionary of English v.0.48:

Punctilious \Punc*til"ious\ (-y[u^]s), a. [Cf. It. puntiglioso,
   Sp. puntilloso.]
   Attentive to punctilio; very nice or exact in the forms of
   behavior, etiquette, or mutual intercourse; precise; exact in
   the smallest particulars. "A punctilious observance of divine
   laws." --Rogers. "Very punctilious copies of any letters."
   --The Nation.
   [1913 Webster]

         Punctilious in the simple and intelligible instances of
         common life.                             --I. Taylor.
   [1913 Webster] -- Punc*til"ious*ly, adv. --
   Punc*til"ious*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

punctiliously
    adv 1: in a punctilious manner; "he launched into a long history
           of the birth of communism, giving credit punctiliously to
           the work of Marx and Engels"