Edwardian Corset Cover sometimes called an under bodice. I think this was all part of a trousseau set made by Hilda Thompson as it does bear a label with her name and I would think dates to early 1900s.  It is made from a very fine cotton and has very pretty lace scallop detail with embroidered panels above, deep lace neck edging which would have had ribbon threaded through.  It is fastened with tiny mother of pearl buttons and has a cotton draw string at the waist. There is a tiny bit of damage where the lace has become detached on the first right hand scallop but this would be easily fixed. Given the age it is in remarkably good condition. This was very difficult to photograph due to the full front but I hope you can see all the detail. The picture of the back shows the lace folded down but this would I think stand up.  PLEASE NOTE WHILST THE WAIST IS QUITE SMALL AS IS THE BACK THE FRONT IS FOR A FULLER FIGURE.
Dimensions these are all approximate:
Waist 70cm
Front chest measurement from side seam to front opening: 40cm this equates to 80cm across the front
Back chest measurement seam to seam: 40cm 
Length top of back neck lace edge to bottom back hem: 36cm
Armhole shoulder to side seam :16cm