Merriam-Webster Collegiate Dictionary - unnerve

 transitive verb  Date: 1601  1. to deprive of courage, strength, or steadiness  2. to cause to become nervous ; upset  • unnervingly adverb Synonyms:  ~, enervate, unman, emasculate mean to deprive of strength or vigor and the capacity for effective action. ~ implies marked often temporary loss of courage, self-control, or power to act ~d by the near collision. enervate suggests a gradual physical or moral weakening (as through luxury or indolence) until one is too feeble to make an effort a nation's youth enervated by affluence and leisure. unman implies a loss of manly vigor, fortitude, or spirit a soldier unmanned by the terrors of battle. emasculate stresses a depriving of characteristic force by removing something essential an amendment that emasculates existing safeguards.