Dressing Gown - a robe worn in the bedroom or dressing room literally before or while dressing. Always a long sleeved and ankle garment, often in the wrap style with sash, although it has been seen with a button front. The style often is derived from the men's robe style, with shawl collar, cuffs and tie belt. Over time, they were made in heavier fabrics suitable for general at home wear. The lines tend to follow current fashion.

40's Satin Dressing Gown 
Courtesy of alonesolo/fashiontales

Negligee - from the 19^th C, a loose fitting , attractive robe worn informally at home. Usually trimmed with lace or ribbon, this was worn for rest with out a corset, or over a loosened corset. Supplanted by the tea gown in the early 1900s, it is now a feminine dressing gown in sheer fabrics.

1970s Zandra Rhodes Negligee courtsey artisannes

Peignoir - from the French ‘peign' to comb. Originally a combing jacket worn over undergarments while dressing the hair. By the late 19^th and 20^th C , became a lightweight, often sheer robe worn over nightwear or undergarments in the bedroom. Always a loose garment with a tie at the neck and an open front. Worn in various fabrics from as early as the 16^th C.

Peignoir set: Robe with pale pink ribbon, embroidered roses and puff sleeves. Night gown in a Grecian style with puff sleeves, gathered bodice and pale pink ribbon woven through the embroidered waist line. All edges are done in a heavy picot stitching
Courtesy of alonesolo/fashiontales