Jolly Roger moves pirates on the high seas, as it's the most important of its kind
I believe the answer is:
flagship
'jolly' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for flagship that I've seen before include "Pre-eminent item" , "leading product" , "Best of its kind; admiral's craft" , "leader of fleet" , "It carries the commander of the fleet" .)