Unnerve, enervate, unman, emasculate can all mean to deprive of strength or vigor and of the capacity for endurance, overcoming difficulties, or making progress.
Unnerve implies marked loss of courage, steadiness, and self-control or of power to act or fight usually as a result of some calamity or sudden shock.
Enervate implies a more gradual physical or moral weakening or dissipation of one’s strength until one is too feeble to make effort; usually the term implies a weakening of moral fiber under the influence of such debilitating factors as luxury, indolence, or effeminacy.
Unman implies loss of manly fortitude or spirit; it often suggests a shameful reduction to tears, tremors, extreme timidity, or other state regarded as womanish.
Emasculate (see also STERILIZE 1 ) implies a loss of essential or effective power especially by the removal of something (as a factor or a condition) which has made for strength (as of a person, a group, or a law).