The definition of insuperable is an obstacle that cannot be overcome.(adjective)
If your boss absolutely forbids you from going on a trip, this is an example of an insuperable obstacle to you going on the trip.
See insuperable in Webster's New World College Dictionary
Origin: ME < L insuperabilis
See insuperable in American Heritage Dictionary 4
Origin: Middle English
Origin: , from Old French
Origin: , from Latin īnsuperābilis
Origin: : in-, not; see in-1
Origin: + superābilis, superable; see superable.
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