Memorable saying (6)
I believe the answer is:
byword
'memorable saying' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for byword that I've seen before include "One pointed at as exemplar" , "Person or thing spoken of as notable example" , "Slogan; paragon" , "Outstanding example or embodiment of something" , "Well-known example of something" .)