Other forms: coolheadedly
If you're coolheaded, you tend to stay calm and unruffled, even when something upsetting happens. One quality of a good teacher is the ability to stay coolheaded at all times.
People who can stay in control of their emotions, who don't tend to get overly excited, worried, or angry, are coolheaded. The most coolheaded debater often comes out ahead, and a coolheaded leader can keep people safe during a disaster or emergency, calmly leading them to safety. The sense of cool that's implied in coolheaded — "self-control or composure" — is relatively new, dating from the late 20th century.