The Collaborative International Dictionary of English v.0.48:

Sutra \Su"tra\, n.; pl. Sutras. [Skr. s?tra a thread, a string
   of rules; an aphorism; fr. siv to sew.]
   1.
      (a) A precept; an aphorism; a brief rule.
      (b) A collection of such aphorisms.
          [1913 Webster]

   2. pl. A body of Hindoo literature containing aphorisms on
      grammar, meter, law, and philosophy, and forming a
      connecting link between the Vedic and later Sanscrit
      literature. --Balfour (Cyc. of India).
      [1913 Webster]

WordNet (r) 3.0 (2006):

sutra
    n 1: a rule or aphorism in Sanskrit literature or a group of
         aphoristic doctrinal summaries prepared for memorization