1. Difficult to burn
   - fire-retardant, fire-resistant, fire-resistive

See also: incombustible, noncombustible

• 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
• unacceptableness
• unacceptably
• unaccepted
• unaccessible
• unaccommodating
• unaccompanied