1. Not easily solved
   "public finance...had long presented problems unsolvable or at least unsolved"
   - insolvable, unsoluble, unresolvable

See also: insoluble

• nonharmonic
• nonhereditary
• nonheritable
• nonhierarchic
• nonhierarchical
• nonhuman
• nonillion
• nonimitative
• nonimmune
• nonindulgence
• nonindulgent
• nonindustrial
• noninfectious
• noninflammatory
• noninheritable
• noninstitutional
• noninstitutionalised
• noninstitutionalized
• nonintegrated
• nonintellectual
• noninterchangeable
• noninterference
• nonintersecting
• nonintervention
• noninvasive