The Collaborative International Dictionary of English v.0.48:

Leisure \Lei"sure\ (l[=e]"zh[-u]r; 135), n. [OE. leisere,
   leiser, OF. leisir, F. loisir, orig., permission, fr. L.
   licere to be permitted. See License.]
   1. Freedom from occupation or business; vacant time; time
      free from employment.
      [1913 Webster]

            The desire of leisure is much more natural than of
            business and care.                    --Sir W.
                                                  Temple.
      [1913 Webster]

   2. Time at one's command, free from engagement; convenient
      opportunity; hence, convenience; ease.
      [1913 Webster]

            He sighed, and had no leisure more to say. --Dryden.
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   At leisure.
      (a) Free from occupation; not busy.
      (b) In a leisurely manner; at a convenient time.
          [1913 Webster]

WordNet (r) 3.0 (2006):

at leisure
    adv 1: in an unhurried way or at one's convenience; "read the
           manual at your leisure"; "he traveled leisurely" [syn:
           at leisure, leisurely]