Daybed and Sofa bed

Daybed noun - An armless couch; a seat by day and a bed by night.

Sofa bed and daybed are semantically related in sofa topic. In some cases you can use "Sofa bed" instead a noun "Daybed", when it comes to topics like couch.

Sofa bed noun - A sofa that can be converted into a bed.

Daybed and sofa bed are semantically related in couch that becomes bed topic. You can use "Daybed" instead a noun phrase "Sofa bed".