The Collaborative International Dictionary of English v.0.48:

Freshen \Fresh"en\, v. i.
   1. To grow fresh; to lose saltness.
      [1913 Webster]

   2. To grow brisk or strong; as, the wind freshens.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Freshen \Fresh"en\, v. t. [imp. & p. p. Freshened; p. pr. &
   vb. n. Freshening]
   1. To make fresh; to separate, as water, from saline
      ingredients; to make less salty; as, to freshen water,
      fish, or flesh.
      [1913 Webster]

   2. To refresh; to revive. [Obs.] --Spenser.
      [1913 Webster]

   3. (Naut.) To relieve, as a rope, by change of place where
      friction wears it; or to renew, as the material used to
      prevent chafing; as, to freshen a hawse. -- Totten.
      [1913 Webster]

   To freshen ballast (Naut.), to shift Or restore it.

   To freshen the hawse, to pay out a little more cable, so as
      to bring the chafe on another part.

   To freshen the way, to increase the speed of a vessel.
      --Ham. Nav. Encyc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

freshen
    v 1: make (to feel) fresh; "The cool water refreshed us" [syn:
         refresh, freshen]
    2: become or make oneself fresh again; "She freshened up after
       the tennis game" [syn: freshen, refresh, refreshen,
       freshen up]
    3: make fresh again [syn: refresh, freshen, refreshen]
       [ant: fag, fag out, fatigue, jade, outwear, tire,
       tire out, wear, wear down, wear out, wear upon,
       weary]