From Latin pl ā num (“ flat surface ”), a noun use of the neuter of pl ā nus (“ plain ”). The word was introduced in the 17th century to distinguish the geometrical senses from the other senses of plain.
副詞 plainly (comparative plainlier or more plainly, superlative plainliest or most plainly) In a plain manner; simply; basically. She decorated the room plainly but neatly.
