This is the 5998th most frequent Russian word.
слегка
Slightly; a little.
The word 'slightly' is used to describe a minor degree of the action—smiled just a little.
Она слегка улыбнулась.
She smiled slightly.
Here, 'slightly' modifies 'warm' to indicate a small and not intense level of heat.
Кофе был слегка тёплым.
The coffee was slightly warm.
In this sentence, 'slightly' expresses the subtle nature of the sound made by the dress.