adjective Not decorated or elaborate; simple or ordinary in character. (good plain food) (of a person) having no pretensions; not remarkable or special. (a plain, honest man with no nonsense about him) Easy to perceive or understand; clear. (the advantages were plain to see) (of a person) not beautiful or attractive. (the dark-haired, rather plain woman) Sheer; simple (used for emphasis) (the main problem is just plain exhaustion) Denoting or relating to a type of knitting stitch produced by putting the needle through the front of each stitch from left to right.