It is an adjective.
Meaning :insuperable.It means incapable of being overcome or conquered i.e. whose power more than the rest.It refers to those things or situations which are not possible to vanquish or deal with.
Root of the word : super/sur = above
Synonyms: insoluble, impossible, intractable, undefeatable, overwhelming
Antonyms : easy,attainable, beatable, defeatable, possible, surmountable
insurmountability , insurmountableness - noun
insurmountably - adverb
1)Most of the problems we consider insurmountable can be solved with a bit of determination.
2)She is stressed out thinking of the insurmountable difficulties.
3)I have been in situations which are more of insurmountable danger than this.
4)These days, youth's routine habits are insurmountable to deal with.