Move up and down or back and forth (6)
I believe the answer is:
seesaw
I believe this clue is a double definition.
'move up and down' is the first definition.
(synonyms)
'back and forth' is the second definition.
(thesaurus)
(Other definitions for seesaw that I've seen before include "Plank children play on" , "Alternate" , "that has its ups and downs" , "Rise and fall" , "Playground device" .)