The Collaborative International Dictionary of English v.0.48:

Coussinet \Cous"si*net`\ (k??s"s?-n?t`), n. [F., dim. of coussin
   cushion. See Cushionet.] (Arch.)
   (a) A stone placed on the impost of a pier for receiving the
       first stone of an arch.
   (b) That part of the Ionic capital between the abacus and
       quarter round, which forms the volute. --Gwilt.
       [1913 Webster]