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.
協会:きょうかい: border???
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.