1. Concave on both sides
   - biconcave

See also: concave

• Ummah
• ump
• umpirage
• umpire
• umpteen
• umpteenth
• umptieth
• umteen
• umteenth
• UN agency
• un-
• un-American
• un-come-at-able
• una corda
• unabashed
• unabashedly
• unabated
• unable
• unable to help
• unabridged
• unabridged dictionary
• unabused
• unaccented
• unacceptability
• unacceptable