1. Hard as granite
   - granitic, rocklike, stony

See also: hard

• Underground Railroad
• Underground Railway
• undergrow
• undergrowth
• underhand
• underhanded
• underhandedly
• underhung
• underivative
• underived
• underlay
• underlayment
• underlet
• underlie
• underline
• underling
• underlip
• underlying
• undermanned
• undermentioned
• undermine
• undermost
• underneath
• undernourish
• undernourished