Plain

adjective:
1. Clearly revealed to the mind or the senses or judgment
(usage: made his meaning plain; it is plain that he is no reactionary; in plain view)
2. Not elaborate or elaborated; simple
(usage: plain food; stuck to the plain facts; a plain blue suit; a plain rectangular brick building)
3. Lacking patterns especially in color
4. Not mixed with extraneous elements
(usage: plain water)
5. Free from any effort to soften to disguise
(usage: the plain and unvarnished truth)
6. Lacking embellishment or ornamentation
(usage: a plain hair style)
7. Lacking in physical beauty or proportion
(usage: a plain girl with a freckled face)

Noun:
1. Extensive tract of level open land
(Usage: they emerged from the woods onto a vast open plain"
2. A basic knitting stitch

Adverb:
1. Unmistakably ('plain' is often used informally for 'plainly')
(Usage: he is plain stubborn)

Verb:
1. Express complaints, discontent, displeasure, or unhappiness

Synonyms:
Apparent
Apparently
Bare
Champaign
Complain
Evident
Evidently
Field
Homely
Kick
Knit
Knit Stitch
Kvetch
Manifest
Manifestly
Obviously
Patent
Patently
Plain Stitch
Plainly
Quetch
Sheer
Sound Off
Spare
Unembellished
unmingled
Unmistakable
Unmistakeable
Unmixed
Unornamented
Unpatterned
Unvarnished