What could be Bangkok hotel’s sound promotional material (3-2)
I believe the answer is:
tie-in
'material' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I don't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tie-in that I've seen before include "Book linked to TV or film production" , "commercial extra" , "Make a link (with)" , "Item linked with popular film, programme etc" , "Relationship" .)