four score: a score is twenty, four score equals eighty
The word score originates from Old English scoru "twenty," from Old Norse skor "mark, tally", in the sense of a shepherd making a mark on a tally stick when counting sheep. Its use in the Bible, is simply that of a common word at the time of translation then falling into disuse though language change.
fortnight: a unit of time equal to fourteen days, or two weeks. The word derives from the Old English fēowertyne niht, meaning "fourteen nights".
In astronomy, a fortnight is the mean (average) time between a full moon and a new moon (and vice versa) or half a synodic month. This is equal to 14.77 days.