1. superlative form of plain: most simple, basic, or without decoration
2. superlative form of plain: most clear or obvious
3. superlative form of plain: least attractive in appearance

Examples

• She chose the plainest dress in the store.
• This is the plainest explanation of the concept I’ve heard.
• The plainest room in the house was surprisingly comfortable.
• He made the plainest statement about his intentions.
• Of all the designs, this one is the plainest.
• The plainest truth is often the hardest to accept.
• She was considered the plainest of the three sisters.