1. Not brought about by coercion or force
   - uncoerced, willing 
2. Not resulting from undue effort; not forced
   "a voice with a pleasingly unforced quality"
   - unstrained

See also: effortless, voluntary

• upskill
• upslope
• upstage
• upstager
• upstair
• upstairs
• upstanding
• upstart
• upstate
• upstream
• upstroke
• upsurge
• upsweep
• upswept
• upswing
• upsy-daisy
• uptake
• upthrow
• upthrust
• uptick
• uptight
• uptil
• uptime
• Upton Beall Sinclair
• Upton Sinclair