unattainable (adj.)

• impenetrable
• impervious
• impracticable
• impractical
• inaccessible
• infeasible
• inoperable
• insuperable
• insurmountable
• un-come-at-able
• unaccessible
• unachievable
• unapproachable
• unavailable
• undiscoverable
• undoable
• unfeasible
• ungetatable
• unobtainable
• unprocurable
• unreachable
• unrealizable
• unsurmountable
• unworkable