The Collaborative International Dictionary of English v.0.48:

Therein \There*in"\, adv.
   In that or this place, time, or thing; in that particular or
   respect. --Wyclif.
   [1913 Webster]

         He pricketh through a fair forest,
         Therein is many a wild beast.            --Chaucer.
   [1913 Webster]

         Bring forth abundantly in the earth, and multiply
         therein.                                 --Gen. ix. 7.
   [1913 Webster]

         Therein our letters do not well agree.   --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

therein
    adv 1: (formal) in or into that thing or place; "they can read
           therein what our plans are" [syn: therein, in this,
           in that]