I just discovered, via aldiboronti at Wordorigins, the expression a pair of stairs, used to mean (in the OED’s words) ‘A set or flight of stairs or steps; (also) a portable set of steps.’ It strikes me as deeply counterintuitive, and I’m pretty sure I’ve never heard or seen it, but it clearly used to be in common use; here are the OED citations:
c1450 J. CAPGRAVE Solace of Pilgrims (Bodl. 423) 77 Thann go we down on a peyr greces in to a chapel thei clepe ierlm.
1530 J. PALSGRAVE Lesclarcissement 182 Vngz degrez, a payre of stayres.
1602 H. PLATT Delightes for Ladies sig. H3v, A maide that fell downe a paire of staires.
1628 J. EARLE Micro-cosmogr. xiii. sig. C10v, A Tauerne Is a degree, or (if you will) a paire of stayres aboue an Alehouse.
1684 Philos. Trans. (Royal Soc.) 14 443 Being.. not able.. to have past through a Gallery down a pair of Stairs into the Court.
1730 Inventory R. Woolley’s Goods 11 A Pair of wooden Steps.
1755 in J. A. Picton City of Liverpool: Select. Munic. Rec. II. 155 A breast wall and pair of steps from the shore or road up to the Ladies’ Walk.
1761 G. COLMAN in St. James’s Chron. 18 June 1/2, I could as easily have scaled the Monument, as have come at the Tip of her Chin without the Help of a Pair of Steps.
1839 DICKENS Nicholas Nickleby xli. 402 An old black velvet cap, which, by slow degrees, as if its wearer were ascending a ladder or pair of steps, rose above the wall.
1884 J. EASTWOOD & W. A. WRIGHT Bible Word-bk. (ed. 2) s.v., We still speak of a ‘pair’ of steps or stairs.
1903 W. D. HOWELLS Lett. Home v. 33 It all ended.. in our finding these two rooms, five pair up, in an apartment with respectable people who are glad to let them.
1923 Times 4 Dec. 16 (caption) Mr. Lloyd George is standing on a pair of steps steadied by porters.
1928 A. E. PEASE Dict. Dial. N. Riding Yorks. 92/2 Pair of stairs, the usual term for a ‘flight’ of stairs or a staircase.
1991 B. ALDISS Frankenstein Unbound (BNC) xx. 172, I.. seized a pair of steps, used to reach the higher shelves; I dragged the steps to the middle of the room.
1995 Daily News (N.Y.) (Nexis) 16 Oct. 20 The lines snaked around the block and down a pair of stairs, into a large exhibition hall.
I’m quite sure they’ve misunderstood the last quote, which must refer to two parallel staircases. I presume some of you have seen the expression used (e.g., in Dickens), but do any of you use it yourselves, or know someone who does?
(Oddly, a pair of arrows means three of them, or did traditionally: “Now chiefly… with reference to the ceremonial obligations of the Royal Company of Archers.”)