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):

punctilious
    adj 1: marked by precise accordance with details; "meticulous
           research"; "punctilious in his attention to rules of
           etiquette" [syn: meticulous, punctilious]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "punctilious":
   accurate, active, attentive, careful, censorious, choicy, choosy,
   close, compliant, conforming, conscientious, conscionable,
   constant, conventional, correct, critical, delicate, demanding,
   detailed, devoted, devout, discriminating, discriminative, duteous,
   dutiful, exact, exacting, exigent, exquisite, faithful, fastidious,
   fine, finical, finicking, finicky, formal, fussy, heedful, loyal,
   methodical, meticulous, mindful, minute, narrow, nice, observant,
   orderly, overconscientious, overscrupulous, painstaking,
   particular, perfectionistic, picky, practicing, precious, precise,
   precisian, precisianistic, precisionist, precisionistic, priggish,
   prudish, punctual, puristic, puritanic, refined, regardful,
   religious, rigid, rigorous, scrupulous, scrutinizing, selective,
   sensitive, strict, subtle, tender-conscienced, true