COOLHEADED

cool, coolheaded, nerveless

(adjective) marked by calm self-control (especially in trying circumstances); unemotional; “play it cool”; “keep cool”; “stayed coolheaded in the crisis”; “the most nerveless winner in the history of the tournament”

Source: WordNet® 3.1

Etymology

Adjective

coolheaded (comparative more coolheaded, superlative most coolheaded)

Having an even temper; calm and collected

Antonyms

• hotheaded

• reckless

Source: Wiktionary

Cool"-head`ed, a.

Definition: Having a temper not easily excited; free from passion.

– Cool"-head`ed*ness, n.

Source: Webster’s Unabridged Dictionary 1913 Edition