indefinable /in-di-fīˈnə-bl/

1. That cannot be defined
2. Hard to identify or describe

• underjawed
• under-jaws
• underkeep
• underkeeper
• underkeepers
• underkeeping
• underkeeps
• underkept
• underking
• underkingdom
• underkingdoms
• underkings
• underlaid
• underlain
• underlap
• underlapped
• underlapping
• underlaps
• underlay
• underlayer
• underlayers
• underlaying
• underlays
• underlease
• underleased