The Collaborative International Dictionary of English v.0.48:

Sexual \Sex"u*al\, a. [L. sexualis, fr. sexus sex: cf. F.
   sexuel.]
   Of or pertaining to sex, or the sexes; distinguishing sex;
   peculiar to the distinction and office of male or female;
   relating to the distinctive genital organs of the sexes;
   proceeding from, or based upon, sex; as, sexual
   characteristics; sexual intercourse, connection, or commerce;
   sexual desire; sexual diseases; sexual generation.
   [1913 Webster]

   Sexual dimorphism (Biol.), the condition of having one of
      the sexes existing in two forms, or varieties, differing
      in color, size, etc., as in many species of butterflies
      which have two kinds of females.

   Sexual method (Bot.), a method of classification proposed
      by Linnaeus, founded mainly on difference in number and
      position of the stamens and pistils of plants.

   Sexual selection (Biol.), the selective preference of one
      sex for certain characteristics in the other, such as
      bright colors, musical notes, etc.; also, the selection
      which results from certain individuals of one sex having
      more opportunities of pairing with the other sex, on
      account of greater activity, strength, courage, etc.;
      applied likewise to that kind of evolution which results
      from such sexual preferences. --Darwin.
      [1913 Webster]

            In these cases, therefore, natural selection seems
            to have acted independently of sexual selection.
                                                  --A. R.
                                                  Wallace.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sexual
    adj 1: of or relating to or characterized by sexuality; "sexual
           orientation"; "sexual distinctions"
    2: having or involving sex; "sexual reproduction"; "sexual
       spores" [ant: asexual, nonsexual]
    3: involved in a sexual relationship; "the intimate (or sexual)
       relations between husband and wife"; "she had been intimate
       with many men"; "he touched her intimate parts" [syn:
       intimate, sexual]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "sexual":
   amative, amatory, amorous, animal, aphrodisiomaniacal, ardent,
   bawdy, bodily, caressive, carnal, clitoromaniacal, concupiscent,
   coquettish, coy, desirous, dirty, earthy, erogenic, erogenous,
   erotic, eroticomaniacal, erotogenic, erotomaniacal, fleshly,
   flirtatious, flirty, gametic, gamic, genital, goatish,
   gynecomaniacal, heterosexual, horny, hot, hysteromaniacal,
   impassioned, ithyphallic, lascivious, lecherous, lewd, libidinal,
   libidinous, lickerish, loverlike, loverly, lubricious, lustful,
   nuptial, nymphomaniacal, obscene, oversexed, passionate, physical,
   potent, priapic, procreant, procreative, propagative, prurient,
   randy, reproductive, salacious, satyric, seminal, sensual,
   sensuous, sex, sexed, sexlike, sexy, spermatic, spermatozoal,
   spermatozoan, spermatozoic, spermic, sporal, sporogenous, sporoid,
   sporous, straight, undersexed, venereal, voluptuous