Real Dictionary

catchword
countable noun: A catchword is a word or phrase that becomes popular or well-known, for example, because it is associated with a political campaign.

catchword in American English
the first word of a book page, printed in the lower right-hand corner of the preceding page to catch the binder's eye
noun: a memorable or effective word or phrase that is repeated so often that it becomes a slogan, as in a political campaign or in advertising a product

catchword in British English
noun: a word or phrase made temporarily popular, esp by a political campaign; slogan