Crossword Genius

Coalasced skirts for evening parties (8,7)

Ross

I believe the answer is:

cocktail dresses

I'm a little stuck... Click here to teach me more about this clue!

'parties' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.
Want a hint initially instead of a full solution? Install my app