To a degree, certainly, they're swamping popular holiday destination (6)
I believe the answer is:
greece
'popular holiday destination' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'to a degree certainly they're swamping' is the wordplay.
'GREECE' is hidden within the letters.
But, I am unsure how the hidden word is indicated.
Can you help me to learn more?
(Other definitions for greece that I've seen before include "Mediterranean republic" , "in E" , "Country of southern Europe" , "Southern European country" , "EU country" .)