1. With no problems or difficulties
   "put the plans into effect quickly and smoothly"
   - swimmingly 
2. In a smooth and diplomatic manner
   "'And now,' he said smoothly, 'we will continue the conversation'"

See also: smooth

• decrease
• decreased
• decreasing
• decreasing monotonic
• decree
• decree absolute
• decree nisi
• decreed
• decrement
• decrepit
• decrepitate
• decrepitation
• decrepitude
• decrescendo
• decrescent
• decretal
• decrier
• decriminalisation
• decriminalise
• decriminalization
• decriminalize
• decry
• decrypt
• decryption
• decubitus