The Collaborative International Dictionary of English v.0.48:

Separable \Sep"a*ra*ble\, a. [L. separabilis: cf. F.
   s['e]parable.]
   Capable of being separated, disjoined, disunited, or divided;
   as, the separable parts of plants; qualities not separable
   from the substance in which they exist. --
   Sep"a*ra*ble*ness, n. -- Sep"a*ra*bly, adv.
   [1913 Webster]

         Trials permit me not to doubt of the separableness of a
         yellow tincture from gold.               --Boyle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

separably
    adv 1: with possibility of separation or individuation; "the two
           ideas were considered separably" [ant: inseparably]