When Lincoln gave his famous speech, was “score” a common term or was he just being eloquent and poetic?
It goes back to the Bible
In 1863 the Bible would have been expected reading of any literate person in the United States. In fact, it might be the only real book people would ever have read or owned.
That’s a good point.
Perhaps this was so people might mistake his references to the Declaration of Independence were instead to the Constitution and thus support his abolishment of slavery.
I also found the word “fourscore” in a couple of Shakespeare plays. Lincoln was familiar with and influenced by both the King James Bible and Shakespeare.
People still use “score” occasionally, just not in everyday language.
“A dozen a gross and a score
Plus three times the square root of four
Divided by seven
Plus five times eleven
Is nine squared and not a bit more”
There’s also the children’s poem “How many miles to Babylon”, which is still quoted in kids poetry books today:
“How many miles to Babylon
Three score and ten
Can I get there by candlelight?
Yes, and back again
If your heels be nimble and light
You may get there by candlelight”
Wikipedia also cites some early lyrics of Humpty Dumpty that have “Four-score men and four-score more” being unable to put him together again
I also just had a little browse through Project Gutenberg to see if I could catch the flavour of nineteenth-century usage. Jane Austen never seems to use it. But Dickens does pretty frequently, and not in the mouths of particularly “high-falutin” characters. So for what that’s worth … it seems like the sort of thing someone of Lincoln’s era might choose to say without seeming overly florid
Checking a few machine-readable books I have on this laptop, I see Jack London, Adam Smith, Jonathan Swift and Charles Darwin are among many authors who used ‘score.’
Jack London’s Call of the Wild even uses ‘fivescore’ instead of ‘hundred’, as do Shakespeare and Martin Luther King, Jr.
‘Fivescore’ may have been considered more precise than ‘hundred’ since even in some fairly recent contexts ‘hundred’ meant ‘sixscore.’
There are a few languages with roots in base-20 scattered all over the world, but there is a particular concentration in Western Europe: Basque, Celtic, French, English.
This ties with my own experience. “Score” is much more likely to be used by bookmakers and street vendors than opera-goers.
Interesting. Thanks for that. Makes me tempted to use it. 
Spanish and Catalan also have words for “a group of twenty” (veintena / vintena respectively), but they’re not very used; in either language you can have grosses based on scores same as you do based on dozens. But the way grammar works in them means that when you count more than one you do it without generating a new word, whereas in French or English it’s a new word.
There’s a cartoon that appeared in Playboy back in the 1960s that I love. It’s done in 19th century engraving style, and shows Lincoln working on the speech at his desk with scraps of discarded drafts around him. The caption reads something like: “‘Seven dozen plus three years ago…’ No, that doesn’t sound right. ‘a Century minus thirteen years ago…’ No1 Still not right! …”
Remember, Lincoln was not the principal speaker at Gettysburg. He simply made some “dedicatory remarks.” The star of the day was supposed to be Edward Everett, who gave a two-hour speech. Here’s his opening line.
Compared to Everett, Lincoln must have sounded downright folksy.
To his credit, Everett may have been the first person to acknowledge the greatness of Lincoln’'s speech:
BTW, the Gettysburg Address happened 10 fortnights after the battle.
Looking at Lincoln’s contemporaries, I see “score” used in both prose and poetry.
Oliver Wendell Holmes, in a short essay, “Bread and Circuses”, published at the start of the Civil War, uses it twice.
The first is similar to Lincoln’s usage:
“And all sorts of unexpected and unheard-of things, which had lain unseen during our national life of fourscore years, came up and are coming up daily, shaken from their bed by the concussions of the artillery bellowing around us.”
“Does any man really suppose, that, of a score of noble young fellows who have just laid down their lives for their country…”
http://www.gutenberg.org/files/40196/40196-h/40196-h.htm
Henry David Thoreau was notable for using a relatively plain style in comparison to his contemporaries (especially compared to orators like Edward Everett). His short essay “Walking”, delivered as a lecture several times throughout the 1850s and published 1862, uses “score” twice:
“There is in fact a sort of harmony discoverable between the capabilities of the landscape within a circle of ten miles’ radius, or the limits of an afternoon walk, and the threescore years and ten of human life.”
“I might have walked about the foot of the tree for threescore years and ten, and yet I certainly should never have seen them.”
“Score” appears 12 times in the poems of Henry Wadsworth Longfellow; in 8 of those it refers to years:
“When each [man] had numbered more than fourscore years, And Theophrastus, at fourscore and ten”
It also refers to numbers of people:
“Seven hundred and fourscore
Men at arms his livery wore”
Why, that would cover the entire time twixt planting and harvest!
Also, the speech was not originally viewed as eloquent or poetic:
“We pass over the silly remarks of the President,” he wrote in his newspaper. “For the credit of the nation, we are willing that the veil of oblivion shall be dropped over them and that they shall no more be repeated or thought of.”
"Here’s the Chicago Times, a leading Democratic paper: “The cheek of every American must tingle with shame as he reads the silly flat dishwatery utterances of a man who has to be pointed out to intelligent foreigners as the President of the United States.”
Ouch!