What does cool mean?
Cool is a versatile English word with three principal strands of meaning. In its oldest and most literal sense, it describes a moderately low temperature — pleasantly or noticeably cold without being freezing, as when a breeze cools a summer afternoon. From this physical sense developed a figurative use describing emotional restraint: a cool person remains calm, composed, and unruffled, especially under pressure, though the word can also imply an unwelcome distance or lack of warmth in someone's manner. Most distinctively, cool has become the dominant informal term of approval in modern English, denoting something fashionable, impressive, or admirable — a usage that arose in African American vernacular and jazz culture and spread worldwide through popular music and film. The word functions as an adjective, noun, and verb, appearing in common expressions such as 'keep your cool' and 'as cool as a cucumber', and its remarkable endurance as slang has made it one of English's most culturally significant adjectives.
Moderately cold in temperature; calm and composed in manner; informally, fashionable or admirable.
"The evening air turned cool as the sun went down."
The slang sense is informal; thermal and temperament senses suit all registers.
To make something cooler, or to become cooler; figuratively, to become calmer or less intense.
"Let the coffee cool for a minute before you drink it."
Commonly used transitively and intransitively; figurative use appears in phrases like 'tempers cooled'.
A state or quality of being cool; also used in music contexts to denote the relaxed style known as cool jazz.
"The cool of the morning made the walk pleasant."
As a mass noun it usually appears in phrases such as 'the cool of the evening'; otherwise rare.
The slang sense of 'cool' as approval is one of the few words whose popularity actually grew stronger over the 20th century — it went from jazz-age slang to the most durable term of admiration in modern English.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cool
Cool derives from Old English cōl, meaning 'cold or moderately cold', which in turn comes from Proto-Germanic *kōlaz; it shares this Germanic root with Dutch koel and German kühl, and is related to the verb form that became Modern English 'to cool' and the noun 'coolness'. The Old English adjective is cognate with the base of the related verb colan, 'to become cold'. The figurative slang sense meaning 'excellent or fashionable' emerged much later, gaining traction in African American communities and jazz culture during the early twentieth century before becoming mainstream by the mid-century. A now-rare derivative, 'coolth' (meaning pleasant coolness), was formed on the analogy of 'warmth'.
Related word forms
How cool is actually used
The adjective spans registers: its thermal sense is neutral and formal-appropriate, while its sense meaning 'fashionable' is informal and colloquial. The figurative senses of emotional composure ('a cool head') are positive, but 'cool' can also carry a negative connotation of aloofness or unfriendliness when describing someone's manner. As a slang term it has shown unusual staying power compared with other fashion words like 'groovy'.
Easily confused with cool
Kool is a brand name (notably Kool-Aid), not a standard English word; 'cool' is the correct spelling in all standard usage.