Drapey J. Crew silk blouse, likely from the '00s or '10s. 

Tunic-length with side slits, mandarin collar, and loose, kimono-like 3/4 length sleeves. Featherweight. 

Moss-olive green color; close-up photos are most color-accurate.

Size x-small. Measures 21" pit-to-pit, 30.5" shoulder to hem (back, longest point), and 8.5" sleeve (armpit to wrist).