attacker

transitive verb

1. to use force against in order to harm; start a fight with; strike out at with physical or military force; assault
2. to speak or write against, esp. with vigor; criticize, denounce, censure, etc.
3. to begin working on energetically; undertake (a problem, task, etc.) vigorously
4. to begin acting upon harmfully or destructively: the disease attacked him suddenly

intransitive verb

noun

1. the act of attacking
2. any hostile offensive action, esp. with armed forces; onslaught
3. the onset of a disease, or the recurrence of a chronic disease
4. a beginning of any task, undertaking, etc.
5. act or manner of such beginning
6. Music promptness and precision in beginning a passage or phrase