The Collaborative International Dictionary of English v.0.48:

Instimulate \In*stim"u*late\, v. t. [Pref. in- not + stimulate.]
   Not to stimulate; to soothe; to quiet. [Obs.] --Cheyne.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Instimulate \In*stim"u*late\, v. t. [L. instimulatus, p. p.
   instimulare to stimulate. See 1st In-, and Stimulate.]
   To stimulate; to excite. [Obs.] --Cockeram.
   [1913 Webster]