Somewhat shocking piece of pottery? (3)
I believe the answer is:
Here is my best explanation:
'pottery?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'somewhat shocking piece' is the wordplay.
'somewhat shocking' becomes 'ja' (I am not sure about this - if you are sure you should believe this answer much more).
'piece' becomes 'r' (abbreviation for Rook).
'of' acts as a link.
(Other definitions for jar that I've seen before include "Storage container", "Beer", "Wide-mouthed container", "drink", "Jolt with glass container", "Pint glass of beer, perhaps", "Container; be incongruous", "(Jam) pot", "Disturbing effect" and "Vessel; sudden impact".)