The Collaborative International Dictionary of English v.0.48:

Relax \Re*lax"\ (r?-l?ks"), v. t. [imp. & p. p. Relaxed
   (-l?kst"); p. pr. & vb. n. Relaxing.] [L. relaxare; pref.
   re- re- + laxare to loose, to slacken, from laxus loose. See
   Lax, and cf. Relay, n., Release.]
   1. To make lax or loose; to make less close, firm, rigid,
      tense, or the like; to slacken; to loosen; to open; as, to
      relax a rope or cord; to relax the muscles or sinews.
      [1913 Webster]

            Horror . . . all his joints relaxed.  --Milton.
      [1913 Webster]

            Nor served it to relax their serried files.
                                                  --Milton.
      [1913 Webster]

   2. To make less severe or rigorous; to abate the stringency
      of; to remit in respect to strenuousness, earnestness, or
      effort; as, to relax discipline; to relax one's attention
      or endeavors.
      [1913 Webster]

            The statute of mortmain was at several times relaxed
            by the legislature.                   --Swift.
      [1913 Webster]

   3. Hence, to relieve from attention or effort; to ease; to
      recreate; to divert; as, amusement relaxes the mind.
      [1913 Webster]

   4. To relieve from constipation; to loosen; to open; as, an
      aperient relaxes the bowels.
      [1913 Webster]

   Syn: To slacken; loosen; loose; remit; abate; mitigate; ease;
        unbend; divert.
        [1913 Webster]

WordNet (r) 3.0 (2006):

relaxed
    adj 1: without strain or anxiety; "gave the impression of being
           quite relaxed"; "a relaxed and informal discussion" [ant:
           tense]

Moby Thesaurus II by Grady Ward, 1.0:

211 Moby Thesaurus words for "relaxed":
   Bohemian, affable, ambling, at ease, at home, at rest, bagging,
   baggy, blank, blankminded, blase, breezy, calm, carefree, careless,
   casual, cautious, circumspect, claudicant, common, composed, cool,
   coolheaded, cordial, crawling, creeping, creeping like snail,
   culpably negligent, dangling, degage, deliberate, derelict,
   devil-may-care, drooping, easy, easygoing, empty, empty-headed,
   faltering, familiar, fatuous, flabby, flaccid, flagging, flapping,
   flexuous, flimsy, floppy, folksy, foot-dragging, free and easy,
   gentle, gracious, gradual, halting, hanging, happy-go-lucky,
   hasteless, haymish, hobbled, hobbling, homely, homey, idle,
   impotent, imprecise, inactive, inadvertent, inane, inattentive,
   incogitant, indifferent, indolent, inexcitable, informal,
   insouciant, irregular, laissez-faire, languid, languorous, lax,
   lazy, leisurely, lenient, limp, limping, loose, low-pressure,
   lumbering, mellow, mild, moderate, natural, neglectful, neglecting,
   negligent, nerveless, nirvanic, nonchalant, noninterfering,
   nonrestrictive, oblivious, off-guard, offhand, offhanded,
   overindulgent, overly permissive, overpermissive, pacific, passive,
   peaceful, permissive, plain, poking, poky, procrastinating,
   quietistic, reluctant, remiss, rickety, rock-steady, rubbery,
   sauntering, scamping, serene, shaky, shuffling, simple, sinuous,
   skimping, slack, slighting, slipshod, sloppy, slothful, slow,
   slow as death, slow as molasses, slow as slow, slow-crawling,
   slow-foot, slow-going, slow-legged, slow-moving, slow-paced,
   slow-poky, slow-running, slow-sailing, slow-stepped, sluggish,
   slurring, snail-paced, snaillike, sociable, soft, staggering,
   steady, steady-handed, steady-nerved, steel-nerved, streaming,
   strolling, strong-nerved, tentative, thoughtfree, thoughtless,
   toddling, tortoiselike, tottering, tranquil, trudging, turtlelike,
   unaffected, unassuming, unblenching, unblinking, unceremonious,
   uncircumspect, unconstrained, unconventional, unfaltering,
   unflinching, unfussy, unguarded, unhasty, unhurried, unideaed,
   unintellectual, unnervous, unoccupied, unofficial, unquivering,
   unreasoning, unreserved, unrestrained, unrigorous, unshaken,
   unshaky, unshrinking, unstrained, unstudied, unthinking,
   untremulous, unwary, unwatchful, unwavering, vacant, vacuous,
   waddling, weak, without a tremor