Source : Webster's Revised Unabridged Dictionary (1913)

Unsettle \Un*set"tle\, v. t. [1st pref. un- + settle.]
   To move or loosen from a settled position or state; to unfix;
   to displace; to disorder; to confuse.

Unsettle \Un*set"tle\, v. i.
   To become unsettled or unfixed; to be disordered. --Shak.

Source : WordNet®

unsettle
     v : disturb the composure of [syn: {faze}, {unnerve}, {enervate}]