Jack Robinsonn.
/ˌdʒak ˈrɒbɪns(ə)n/, U.S. /ˌdʒæk ˈrɑbəns(ə)n/ colloquial.
Only in before one can (also could) say Jack Robinson and variants: in a very short time; very quickly or suddenly.
ΚΠ
1763 Beauties of all Mag. Sel. II. 81/1 Before you can say Jack Robinson, locks them fast in a square inch of paper.
1778 F. Burney Evelina III. xxi. 241 I'd do it as soon as say Jack Robinson.
1785 E. Winslow in Winslow Papers 310 Before I could say ‘Jack Robinson’.
1814 M. W. Shelley in E. Dowden Life Shelley (1887) I. 453 The white and flying cloud of noon, that is gone before one can say ‘Jack Robinson’.
1863 London Soc. Nov. 475/2 A native gentleman comes up,..gives a smart bow, and before you can say Jack Robinson, is twirling her round the room.
1903 A. Adams Log of Cowboy vii. 86 Before you could say Jack Robinson our dogies..were running in half a dozen different directions.
1949 E. Goudge Gentian Hill i. vi. 105 Her little white teeth were buried in it before anyone had time to say Jack Robinson.
2016 Nigerian Tribune (Nexis) 4 Nov. Before you can say Jack Robinson, things will begin to move for them positively.
This entry has been updated (OED Third Edition, March 2018; most recently modified version published online March 2022).
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n.1763