Motion formerly carried by marrying Scott and Janis? (6)
I believe the answer is:
joplin
'scott and janis?' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for joplin that I've seen before include "Scott -, US ragtime composer" , "Scott -; Janis -" , "pianist" , "rock singer" .)