This is a word that I have to look up every single time, for I keep confusing it with élan, éclair and en clair and various other French words. My Mac’s dictionary tells me:
brilliant display or effect : she came into prominence briefly but with éclat.
• social distinction or conspicuous success : such action bestows more éclat upon a warrior than success by other means.
The Merriam-Webster online dictionary also provides a pronunciation guide, but I wonder if the Regency-era English followed the general rule that consonants at the end of word are silent, or whether they pronounced it like the English pronounce valet (rather like wallet).
In Chapter 18 of Pride and Prejudice, Elizabeth says to Darcy:
“Both,” replied Elizabeth archly; “for I have always seen a great similarity in the turn of our minds. We are each of an unsocial, taciturn disposition, unwilling to speak, unless we expect to say something that will amaze the whole room, and be handed down to posterity with all the éclat of a proverb.”
To me, it sounds like Elizabeth is saying “handed down to posterity with all the [finality or authority] of a proverb,” although I suppose it could also be replaced with effect.
In Chapter 16 of Emma, the titular character seems to use the word as unwanted attention.
She stopt to blush and laugh at her own relapse, and then resumed a more serious, more dispiriting cogitation upon what had been, and might be, and must be. The distressing explanation she had to make to Harriet, and all that poor Harriet would be suffering, with the awkwardness of future meetings, the difficulties of continuing or discontinuing the acquaintance, of subduing feelings, concealing resentment, and avoiding éclat, were enough to occupy her in most unmirthful reflections some time longer, and she went to bed at last with nothing settled but the conviction of her having blundered most dreadfully.