Plain
As an adjective
Exhaustive
Above board
Abrupt
Absolute
Antiseptic
Apparent
Appreciable
Artless
Audible
Au natural
Austere
Bald
Bare
Barefaced
Black and white
Bleak
Bluff
Bluffy
Blunt
Bluntly
Bright
Broad
Brusk
Brusque
Brusquely
Candy
Candidly
Clarified
Clean
Clean out
Clear
Clear out
Cognizable
Cognoscrible
Comprehensible
Concentrated
Conservative
Crusty
Crystal clear
Curt
Curtly
Decided
Decipherable
Definite
Denuded
Digestible
Discernible
Distinct
Divested
Distinct
Earnest
Earnestly
Earthly
Evident
Explicit
Fair
Fathomable
Filtered
Fine
Forthright
Forthrightly
Foursquare
Frankley
Free heartedly
Free spoken
Fresh
Full bodied
Guileless
Graspable
Gruff
Gruffy
Homely
Honestly
Impertinent
Impolite
Impolitely
Inconsiderate
Inconsiderately
Inconspicuous
Ingenious
Innocent
Intelligible
Knowledgeable
Legible
Lucid
Luculent
Luminous
Manifest
Modest
Muted
Naive
Naked
Natural
Neat
Non ambiguous
Obvious
Open
Opening and shoot
Open heartedly
Openly
Out front
Outspoken
Overt
Palpable
Patent
Pellucid
Perceptible
Perspicuous
Plainspoken
Plain vanilla
Point blank
Pure
Purified
Quiet
Readable
Real
Recognisable
Refine
Rendered
Ringing
Rude
Rudely
Self evident
Self explanatory
Sensible
Severe
Sharp
Simple
Sincere
Sober
Spartan
Stark
Straight
Straightforward
Straightforwardly
Straightforward
Stripped
Strong
Subdued
Tactless
Taintless
Talking turkey
Tangible
Thoughtless
Toned
Toned down
Transparent
Trenchant
Tried
True
Truthful
Truly
Unadorned
Unadulterated
Unaffected
Unalloyed
Unambiguous
Unambivalent
Uncivil
Uncombined
Uncomplicated
Uncontaminated
Uncorrupt
Undecorated
Undefiled
Understated
Undesigned
Undisguised
Undiluted
Undiplomatic
Unembellished
Unequivocal
Ungracious
Unguarded
Unguardedly
Uninhibited
Unmannerly
Unmistakable
Unobtrusive
Unornamented
Unpolluted
Unpretending
Unpretentious
Unreserved
Unreservedly
Unrestrained
Unsophisticated
Unsuitable
Untainted
Unvarnished
Veracious
Visible
Vocal
Vociferous
Well defined