Is this an Oscar De La Renta Gown or Nightgown?

[closet-space]

Hello! I purchased this lovely vintage Oscar De La Renta Crushed Velvet Gown this weekend. The problem is that I can not tell if it is an acutal dress or a nightgown

It is marked as a size 6. No Zippers. Just button closures on the sleeves.

Thanks for your input!

 

[UndoneMrs]

Can you post the label ? Might be with his work for "Swirl" a nice loungewear company.