Republic Sample Floral Dress. Size M

I picked up this dress about 6 years ago in NYC, and I've never worn it. It is in good condition, no stains or rips - nothing! Unusual and very pretty, the material is like a linen crochet, with a lot of open areas, a full, white slip with spaghetti straps is fully attached underneath. High Frill neckline and straight down dress. Long back zip closure 20 inches long. Armpit to armpit is 18 inches. Length is 36 inches. It says M size but I'd say more S to M. There are no inside tags, I'm presuming it's man made material.