leastestadj.n.
/ˈliːstᵻst/, U.S. /ˈlistəst/ Originally regional. Now chiefly humorous.
A. adj.
Smallest, least. Cf. mostest adj.
ΘΚΠ
the world > relative properties > quantity > smallness of quantity, amount, or degree > [adjective] > smallest or slightest
leasteOE
lessest1542
leastesta1794
a1794 M. Palmer Dialogue Devonshire Dial. (1837) 14 I ne'er had the leastest inkling for such a thing.
1827 New-Eng. Galaxy 25 May 1/3 They're all as rich as mud—for they've got ruffles to their shirts, and watch-chains, and don't wear the leastest bit of homespun.
1885 Youth's Compan. 24 Dec. 555/2 There wasn't the leastest thing in it—not the leastest little mite of a scrimp!
1906 ‘M. E. Francis’ Simple Ann. 47 The leastest drap in your tea, just to hearten ye up. It 'ull do ye good.
1998 R. Antoni in S. Brown & J. Wickham Oxf. Bk. Caribbean Short Stories (1999) 409 Leastest thing you could do is take off that wig... You look like a fool.
2010 Pioneer Press (St. Paul, Minnesota) (Nexis) 21 Jan. Here come the wacky Asian carp..Give your line the leastest slack He'll give your head a nasty thwack.
B. n.
With the. The smallest amount or number, the least. Now sometimes opposed to the mostest: see mostest n.
ΘΚΠ
the world > relative properties > quantity > smallness of quantity, amount, or degree > [noun] > least quantity or amount
leasteOE
leastest1862
1862 Boston Herald 24 Nov. I calkerlate I saved three dollars yisterday, at the leastest.
1875 Rochester (Indiana) Union Spy 10 Dec. He was full of mischief, too, and that's what gurls don't object to in the leastest.
1916 J. F. Lynch Advocate 175 I know Mr. Lynch is an able lawyer, but he knows the leastest about doing work around a house of any man I ever saw.
1999 J. Burchill Married Alive xii. 186 Believe me, I'm not the hostess with the mostest, I'm the beastess with the leastest.
2017 @WiseOldFranklin 13 Nov. in twitter.com (O.E.D. Archive) The ideal solution to any problem in any design is to achieve the mostest with the leastest.
This entry has been updated (OED Third Edition, June 2018; most recently modified version published online March 2022).
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adj.n.a1794