a jacket, not worn with matching trousers/pants, often showing the colours or badge of a club, school, team, etc. He was smartly dressed in a blazer and slacks. a school blazer See related entries: School life Word Origin late 19th cent.: from blaze ‘burn brightly’ + -er. The original general sense was ‘a thing that blazes or shines’ (mid 17th cent.), giving rise to the term for a brightly coloured sporting jacket.