from
The Collaborative International Dictionary of English v.0.48
Assiento \As`si*en"to\, n. [Sp. asiento seat, contract or
agreement, fr. asentar to place on a chair, to adjust, to
make an agreement; a (L. ad) + sentar, a participial verb; as
if there were a L. sedentare to cause to sit, fr. sedens,
sedentis, p. pr. of sed?re to sit.]
A contract or convention between Spain and other powers for
furnishing negro slaves for the Spanish dominions in America,
esp. the contract made with Great Britain in 1713.
[1913 Webster]