This is the 9948th most frequent Catalan word.
nadalenca
"Nadalenca" means "related to Christmas" in English.
Here, 'nadalenca' is used as an adjective to describe the song as relating to Christmas.
La cançó nadalenca sona molt bé.
The Christmas song sounds very good.
In this sentence, 'nadalenca' characterizes the theme of the decoration, showing its relation to Christmas.
Decorarem la casa amb temàtica nadalenca.
We will decorate the house with a Christmas theme.
The word 'nadalenc' (masculine form for 'nadalenca') here describes the atmosphere, indicating it pertains to Christmas.