extremus

Extremus, extrema, extremum: the superlative of exterus, "outside", with exterior in the middle. It means both the farthest in space and the last in time, and a third shade, "the worst, the most desperate", grows out of the second.

The construction is the thing to learn. Latin makes the adjective agree with the noun where English wants a partitive: extrema pars agri is not "the extreme part" but "the far end of the field", in extremo libro is "at the end of the book", not "in the last book", and ad extremum is simply "finally". The neuter plural extrema stands alone for the end, the crisis, or death - hence the church's extrema unctio. English extreme, extremity and extremist.