The Collaborative International Dictionary of English v.0.48:

Seah \Se"ah\, n.
   A Jewish dry measure containing one third of an ephah.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Seah
   In land measure, a space of 50 cubits long by 50 broad. In
   measure of capacity, a seah was a little over one peck. (See MEASURE.)