plain

1 plain /ˈpleɪn/ adjective
plainer; plainest
1 plain
/ˈpleɪn/
adjective
plainer; plainest
Britannica Dictionary definition of PLAIN
[also more plain; most plain]
1 
: having no pattern or decoration
2 
: not having any added or extra things
3 
: easy to see or understand
4 
: simple and honest
5 
always used before a noun : complete and total
6 
: not unusual or special in any way : ordinary
7 
: not handsome or beautiful

in plain sight

chiefly US or in plain view
: in a place that is easily seen

plain clothes

: the ordinary clothes of a police officer who is not wearing a uniform
— see also plainclothes

plain sailing

— see sailing

— plainly

adverb

— plainness

noun [noncount]
2 plain /ˈpleɪn/ noun
plural plains
2 plain
/ˈpleɪn/
noun
plural plains
Britannica Dictionary definition of PLAIN
[count]
: a large area of flat land without trees
3 plain /ˈpleɪn/ adverb
3 plain
/ˈpleɪn/
adverb
Britannica Dictionary definition of PLAIN
informal
: truly or completely — used to make a statement or description more forceful