aggression, attack, criticize, polish
攻 centers on forceful action directed at a target: attacking, aggression, or criticizing. The sense of polishing is a natural extension of applying repeated, directed effort to refine something.
攻 combines 工 (work, craft) with 攵 (a hand holding a stick, suggesting action). Together they express the idea of applying effort or force, which developed into attacking and, by extension, polishing through repeated action.
The left side 工 is a tool or work, and the right side 攵 is a hand holding a stick. Picture a worker using a tool to strike or polish something: that forceful, repeated action is 攻.
For コウ, imagine a kō (こう, like 'co-') worker attacking a stubborn stain with a polishing tool: kō -> コウ, and the worker keeps striking until it shines.
attack; assault; raid; onslaught; offensive
capture (of enemy territory); taking (by storm); conquest; attack; assault
to attack; to assault; to assail
swift attack; quick attack; fast break; breakaway
major subject; special study
invasion
suicide attack; kamikaze attack
offense and defense; offence and defence
offensive (movement); aggression
special attack unit; kamikaze unit; suicide squad
offense and defense; offence and defence; batting and fielding
frontal attack
fierce attack
batting first
to invade; to attack; to breach; to penetrate
impregnable
attack; drive; advance; invasion
attack; offence; offense; assault
siege
inundating a castle; flooding a castle