don't go beyond the farthermost (or furthermost) tree.
explored the furthest reaches of space.
extreme caution.
extreme cold.
extreme pleasure.
had traveled to the farthest frontier.
he tried his utmost.
in the uttermost distress.
the utmost tip of the peninsula.
to the last measure of human endurance.
to the utmost degree.
utmost contempt.
whether they were accomplices in the last degree or a lesser one was...to be determined individually.