1. cool (temperature, color, etc.)
2. cool (i.e. calm and collected); cool-headed; cold-hearted
どこからか、クールな声が聞こえてきた。From somewhere, a cool voice could be heard.
3. cool (i.e. fashionable or stylish)
事実だったら、最高にクールな話だ。If it were true, it would be a supremely cool story.
4. course (of medical treatment)
治療の一クール目が終わった。The first course of treatment is over.