The Collaborative International Dictionary of English v.0.48:

libido \li*bi"do\ (l[i^]*b[=e]"d[-o]), n.
   1. Sexual desire; the sexual instinct; the sex drive.
      [PJC]

   2. (Psychoanalysis) Those desires and instinctual energies
      which are derived from the id.
      [PJC] Libken

WordNet (r) 3.0 (2006):

libido
    n 1: (psychoanalysis) a Freudian term for sexual urge or desire

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "libido":
   Amor, Christian love, Eros, Platonic love, admiration, adoration,
   affection, agape, anima, archetypal pattern, archetype, ardency,
   ardor, attachment, blind impulse, bodily love, brotherly love,
   caritas, carnality, charity, coconscious, coldness,
   collective unconscious, concupiscence, conjugal love, conscience,
   conscious self, curiosity, death instinct, desideration, desire,
   devotion, drive, eagerness, ego, ego ideal, ego-id conflict,
   ethical self, faithful love, fancy, fantasy, fervor, flame, flesh,
   fleshliness, fondness, foreconscious, free love, free-lovism,
   frigidity, heart, hero worship, hope, horme, id, idolatry, idolism,
   idolization, impotence, impulse, inborn proclivity, instinct,
   intellectual curiosity, lasciviousness, libidinal energy, like,
   liking, love, lovemaking, lust for learning, marriage,
   married love, mind, motive force, natural instinct,
   natural tendency, need, passion, persona, personality,
   physical love, pleasure, pleasure principle, popular regard,
   popularity, potency, preconscious, primitive self, psyche,
   psychic apparatus, racial unconscious, regard, self, sensuality,
   sentiment, sex, sex drive, sexiness, sexual desire,
   sexual instinct, sexual love, sexual urge, sexualism, sexuality,
   shine, spiritual love, subconscious, subconscious mind,
   subconscious urge, subliminal, subliminal self, submerged mind,
   superego, tender feeling, tender passion, thirst for knowledge,
   truelove, unconscious, unconscious mind, unlearned capacity,
   unreasoning impulse, urge, uxoriousness, vital impulse,
   voluptuousness, want, wanting, weakness, will, will and pleasure,
   wish, wish fulfillment, worship, yearning