The word "同床共枕" is formed by combining the two-character phrases "同床" and "共枕", where "同" means "together" or "same", "床" means "bed", "共" means "together" or "shared", and "枕" means "pillow". Each phrase pairs a sharing verb with a noun, resulting in a literal depiction of sharing a bed and sharing a pillow, which together emphasize physical closeness.