Bubble, essentially (3)
I believe the answer is:
orb
'bubble essentially' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for orb that I've seen before include "Spherical object or shape" , "component of royal regalia" , "Ceremonial globe carried by a monarch" , "Sphere for a sovereign" , "Sovereign artefact" .)