Plain
The word plain is an adjective, an adverb, and a noun
As an adjective
As an adjective the word plain means,
-Not decorated
-Not elaborate
-Simple
-Simple in character
-Basic
-Basic in character
-Without a pattern
-In only one colour
-Bearing no indication to its contents
-Bearing no indication as to its affiliation
-Having no pretensions
-Not remarkable
-Not special
-Easy to perceive
-Easy to understand
-Clear
-Not using concealment
-Not using deception
-Frank
-Sheer
(Of paper)
-Without lines
(Of a person)
-Without special title
-Without status
-Not beautiful
-Not attractive
(Of written or spoken usage)
-Clearly expressed
-Without the use of technical terms
-Without the use of abstruse terms
(Of knitting)
-A type of stitch produced by putting the needle through the stitch from left to right.
As an adverb
As an adverb, the word plain means,
-Clearly
-Unequivocally
And can be used for,
-Emphasis.
As a noun
As a noun the word plain means,
-A large flat area of land with few trees.