Easily remembered (9)
'easily remembered' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for catchy that I've seen before include "(Of a tune) instantly appealing and memorable" , "Of tune, pleasant and easily remembered" , "Attention-grabbing" , "(Of tune) infectious" , "Of tune, pleasant and easy to remember (6)" .)
(Other definitions for memorable that I've seen before include "Catchy" , "noteworthy" , "Special" , "Easily recalled" .)