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.