This is the 3299th most frequent Swedish word.
vacker
Beautiful.
In this sentence, 'vacker' describes the lake ('sjön') as being aesthetically pleasing.
Solen går ner över den vackra sjön.
The sun is setting over the beautiful lake.
Here, 'vacker' is used to describe the appearance of the dress ('klänning') indicating its attractiveness.
Hon hade på sig en vacker klänning på festen.
She wore a beautiful dress at the party.
In this context, 'vacker' refers to the gesture ('gest') as being admirable or noble in character.