The term 'break a sweat' is an idiom that means to work hard or to exert a lot of effort. The crossword solution for this term is 'PERSPIRE, ' which is an 8-letter word meaning to secrete moisture, typically through the pores in the skin, especially as a reaction to heat, physical exertion, or stress. Perspiration is the body's natural way of cooling itself down and is an important part of the body's thermoregulatory system.