The Collaborative International Dictionary of English v.0.48:

Manstealing \Man"steal`ing\, n.
   The act or business of stealing or kidnaping human beings,
   especially with a view to e?slave them.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

MANSTEALING. This word is sometimes used synonymously with kidnapping. The
latter is more technical. 4 Bl. Com. 219.