1. Unmistakably ('plain' is often used informally for 'plainly')
   "You are plainly wrong"
   - obviously, evidently, manifestly, patently, apparently, plain 
2. In a simple manner; without extravagance or embellishment
   "she was dressed plainly"
   - simply

See also: plain

• incognizant
• incognoscible
• incoherence
• incoherency
• incoherent
• incoherently
• incombustible
• income
• income bracket
• income fund
• income statement
• income support
• income tax
• income tax bracket
• income tax return
• incomer
• incoming
• incommensurability
• incommensurable
• incommensurate
• incommode
• incommodious
• incommodiousness
• incommunicable
• incommunicado