The Collaborative International Dictionary of English v.0.48:

Strait-laced \Strait"-laced`\, a.
   1. Bound with stays.
      [1913 Webster]

            Let nature have scope to fashion the body as she
            thinks best; we have few well-shaped that are
            strait-laced.                         --Locke.
      [1913 Webster]

   2. Restricted; stiff; constrained. [R.] --Fuller.
      [1913 Webster]

   3. Rigid in opinion; strict in manners or morals.
      [1913 Webster]

WordNet (r) 3.0 (2006):

strait-laced
    adj 1: exaggeratedly proper; "my straitlaced Aunt Anna doesn't
           approve of my miniskirts" [syn: priggish, prim,
           prissy, prudish, puritanical, square-toed,
           straitlaced, strait-laced, straightlaced,
           straight-laced, tight-laced, victorian]