Definitions of hostility:

• noun:   acts of overt warfare
• noun:   a hostile (very unfriendly) disposition

  Example: "He could not conceal his hostility"

• noun:   the feeling of a hostile person

  Example: "He could no longer contain his hostility"

• noun:   a state of deep-seated ill-will
• noun:   violent action that is hostile and usually unprovoked