the business end of

今日も誰でも知っている単語、"business"、ですが、こんな使い方（慣用句）がある事を初めて知りました。次の文はThe Running Manからの引用です。
The doctor produced a stopwatch from an inside pocket, clicked the business end of his ballpoint pen, and considered a list in front of him.
"the business end of" がボールペンでクリックする部分の事だと言うのは明白ですが、"business" を辞書で見ても適当な説明は見当たりません。 しつこく辞書を見ると慣用句で "the business end of" と言う表現があり、次の説明がありました。
・Oxford English Dictionary: The functional part of a tool, device, or weapon: he found himself facing the business end of six lethal-looking weapons
・McGraw-Hill Dictionary of American Idioms and Phrasal Verbs: the part or end of something that actually does the work or carries out the procedure. Keep away from the business end of the electric drill so you won't get hurt. Don't point the business end of that gun at anyone. It might go off.
日本語にはない表現ですね。