Hostess Gown - from the 1930s - 70s, a dressy full length garment for entertaining, but not as formal as evening wear. Other than the full length, the lines followed current fashion.

Miss Elaine 40's Hostess Gown
Courtesy of memphisvintage

 Housecoat covers a variety of garments. Originally a dressy , yet comfortable coat worn around the house. Often buttoning or zipping at the front. Later in the 20^th C, a more utilitarian front closing shift with pockets and either long or short sleeve worn at home for comfort.

1940s House coat courtesy bigchief178 

Bathrobe - a utilitarian garment able to handle damp, worn either immediately after the bath or over nightgown. Usually in washable, sturdy fabrics such as terry cloth, quilted cottons and manmade fibers.

Pink Quilted 60's Bathrobe with fiber fill
Courtesy of alonesolo/fashiontales