adjective
plainer; -est
[also more ~; most ~]
having no pattern or decoration
not having any added or extra things
easy to see or understand
simple and honest
always used before a noun :complete and total
not unusual or special in any way :ordinary
not handsome or beautiful
in plain sight
or in plain view
chiefly US :in a place that is easily seen
plain clothes
the ordinary clothes of a police officer who is not wearing a uniform
plain sailing
noun
plural plains
[count] :a large area of flat land without trees
adverb
informal :truly or completely