Fleuron must be some rare and deadly gas, yes?
A fleuron can either be a design representing a flower, leaves or leaf:
(that one is used to mark divisions in blocks of type)
or a fleuron can be a twiddly bit of pastry on the top of a pie:
They're both deeply good things as far as I'm concerned.
Spot the Frippet: fleuron. This word comes from the Old French flor, flower.