1. Having a relatively tough outer covering 
2. Insensitive to criticism
   - thick-skinned

See also: insensitive, tough

• upsetting
• upshot
• upside
• upside-down
• upside-down cake
• upsilon
• upskill
• upslope
• upstage
• upstager
• upstair
• upstairs
• upstanding
• upstart
• upstate
• upstream
• upstroke
• upsurge
• upsweep
• upswept
• upswing
• upsy-daisy
• uptake
• upthrow
• upthrust