国境：こっきょう： border between two countries??
境：さかい： boundary - can be used with countries OR property lines of 2 pieces of land. Usually used when talking about crossing a boundary.
縁：ふち： rim or edge of table, cup, picture frame (emphasis is that it's not a point on the edge, it's the ENTIRE edge)
末：すえ： the end of something - usually figurative (end of story!)
際：きわ： border or edge of something- usually used with locations: 'I'm standing on the edge of the ocean, where it meets the shore.'
先：さき： the tip of a sharp thing.
端 ：はし： edge ??? how is this different from kiwa? As opposed to 縁、 端 usually refers to one point on the edge, the most extreme point (i.e. edge of the cliff, tip of the peninsula????)
外れ：はずれ： ONE OF the meanings of 外れ is 'on the edge of something ' (i.e. 'I'm >???')
境界 means border or boundary in the figurative sense - like "this film pushes the envelope of good taste" or "his art blurs the boundary between painting and sculpture". also used in science.