Piece seen seldom in opera houses (6)
I believe the answer is:
domino
'piece' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'seldom in opera houses' is the wordplay.
'houses' says the answer is hidden in the clue (part of the clue houses the answer).
'DOMINO' is hidden within 'seldom in opera'.
'seen' is the link.
Can you help me to learn more?
(Other definitions for domino that I've seen before include "Piece with pips; Fats ---, R&B singer" , "Officers' mess aboard" , "Loose cloak with mask for upper face" , "Rectangular block used in game" , "Spotted piece used in a table game" .)