Diamond tip (4)
I believe the answer is:
rock
This clue might be a double definition.
'diamond' is the first definition.
(thesaurus)
'tip' is the second definition.
The answer and definition can be both to do with motion as well as being verbs in their base form.
Maybe they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for rock that I've seen before include "lull baby to sleep?" , "Sway - very big stone" , "Stagger" , "Edinburgh - -" , "Brighton - (novel); - Hudson" .)