This is the 6837th most frequent Catalan word.
thúy
It seems "thúy" is not a Catalan word. In Vietnamese, "Thúy" is a common given name meaning gentle or pure.
'Thúy' here is a possessive form indicating ownership over the dress described.
El vestit de Thúy és molt bonic.
Thúy's dress is very beautiful.
Here, 'Thúy' is used as a proper noun referring to a specific person or character.
He llegit un conte sobre la princesa Thúy.
I read a story about Princess Thúy.
In this sentence, 'Thúy' specifies the speaker or subject of a quoted or described action.