fin=終わる、境界

infinite / 終わりのない→無限の、計り知れない

cf. There is an infinite number of stars in teh night sky.

define / 完全に境界を引く→定める、定義する

cf. It is difficult to define the border between love and friendship.

confine / 共に境界内にとどめる→制限する、監禁する

cf. Confine your remarks to the matter we are discussing.