Although slogan is derived from a Gaelic word meaning "army cry" and motto from a Latin word meaning "utterance," they are closely related in sense. Each suggests a saying or expression used as a guiding principle or rule of conduct. Slogan specifically means a "catchword" or "catch phrase" used by a political party, fraternity, or school group or in advertising and promotion: "The slogan of this company is 'When better beds are made, we'll make them. '" A motto is usually briefer than a slogan and more likely to express a moral aim or purpose: "The motto of the Boy Scouts of America is 'Be Prepared. '" Words related to slogan and motto, but with shadings of meaning, include maxim, saying, saw, aphorism, catchword, and watchword.
Dictionary of problem words and expressions. Harry Shaw. 1975.