The Collaborative International Dictionary of English v.0.48:

Punctilio \Punc*til"io\ (p[u^][ng]k*t[i^]l"y[-o]), n.; pl.
   Punctilios (-y[=o]z). [It. puntiglio, or Sp. puntillo, dim.
   fr. L. punctum point. See Point, n.]
   A nice point of exactness in conduct, ceremony, or
   proceeding; particularity or exactness in forms; as, the
   punctilios of a public ceremony.
   [1913 Webster]

         They will not part with the least punctilio in their
         opinions and practices.                  --Fuller.
   [1913 Webster]

WordNet (r) 3.0 (2006):

punctilio
    n 1: a fine point of etiquette or petty formality
    2: strict observance of formalities