The continent of China, Siam, etc. (4)
I believe the answer is:
asia
'the continent' is the definition.
(Asia is an example)
'of china siam etc' is the wordplay.
'of' indicates the answer is hidden within the clue.
'ASIA' is hidden in the letters of 'china siam etc'.
(Other definitions for asia that I've seen before include "Populous continent" , "Major land mass" , "lands in the east" , "Continent of the Hindu Kush" , "Largest land-mass" .)