au grand sérieuxadv.
/əʊ ˌɡrɒ̃ ˌsɛrˈjəː/, U.S. /ˌoʊ ˌɡrɑn ˌsɛrˈjə/, /ˌoʊ ˌɡrɑ̃ ˌsɛrˈjə/ Very seriously, in all seriousness. Chiefly in to take (also treat) au grand sérieux. Cf. au sérieux adv.
ΘΚΠ
the mind > attention and judgement > importance > [adverb] > gravely or seriously
gravously1548
heavy1563
capitally1606
seriously1770
au sérieux1836
au grand sérieux1849
gravely1885
1849 W. M. Thackeray Pendennis (1850) I. xvi. 139 Pen..took the matter au grand serieux, with the happy conceit and gravity of youth.
a1865 E. C. Gaskell Wives & Daughters (1866) II. v. 48 You must not go and take me au grand sérieux.
1881 Academy 24 Dec. 469/2 On the whole, the volume seemed to be written au grand sérieux.
1936 C. S. Lewis Allegory of Love iv. 163 They all took Chaucer's love poetry au grand sérieux.
1962 Dumbarton Oaks Papers 16 99 Lacking any discernible trace of humor, he took himself au grand sérieux, did not shun controversy, or hesitate to make his superiority very clear.
2008 Financial Times 2 June 17/5 Cherkaoui demands that it be taken au grand sérieux, even though the monks deploy all the acrobatic verve and merry cries we know from less portentous occasions.
This entry has been updated (OED Third Edition, September 2017; most recently modified version published online December 2021).
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adv.1849