The Collaborative International Dictionary of English v.0.48:

Latent \La"tent\ (l[=a]"tent), a. [L. latens, -entis, p. pr. of
   latere to lie hid or concealed; cf. Gr. lanqa`nein, E.
   lethargy: cf. F. latent.]
   1. Not visible or apparent; hidden; concealed; secret;
      dormant; as, latent springs of action.
      [1913 Webster]

            The evils latent in the most promising contrivances
            are provided for as they arise.       --Burke.
      [1913 Webster]

   2. (Med.) Existing but not presenting symptoms; dormant or
      developing; -- of disease, especially infectious diseases;
      as, the latent phase of an infection.
      [PJC]

   Latent buds (Bot.), buds which remain undeveloped or
      dormant for a long time, but may eventually grow.

   Latent heat (Physics), that quantity of heat which
      disappears or becomes concealed in a body while producing
      some change in it other than rise of temperature, as
      fusion, evaporation, or expansion, the quantity being
      constant for each particular body and for each species of
      change; the amount of heat required to produce a change of
      phase.

   Latent period.
      (a) (Med.) The regular time in which a disease is supposed
          to be existing without manifesting itself.
      (b) (Physiol.) One of the phases in a simple muscular
          contraction, in which invisible preparatory changes
          are taking place in the nerve and muscle.
      (c) (Biol.) One of those periods or resting stages in the
          development of the ovum, in which development is
          arrested prior to renewed activity.
          [1913 Webster]

WordNet (r) 3.0 (2006):

latent heat
    n 1: heat absorbed or radiated during a change of phase at a
         constant temperature and pressure [syn: latent heat,
         heat of transformation]