1. ostentatious display
2. dazzling effect; brilliance
3. brilliant or conspicuous success
4. acclaim, praise, applause
Etymology: French éclat, splinter or fragment, or eclater, to burst out or to splinter.
Most of the definitions date from the late 1600s, but "conspicuous success" dates from the mid 1700s.
In The Gay Divorcee (on TCM tonight), lawyer Egbert Fitzgerald says "with what éclat am I upholding the professional dignity of the firm."