an incendiary mixture of unknown composition, used in warfare in medieval times by Byzantine Greeks.
2.
any of a group of inflammable mixtures; wildfire.
Origin
1820-30
British Dictionary definitions for Greek fire
Greek fire
noun
1.
a Byzantine weapon employed in naval warfare from 670 ad. It consisted of an unknown mixture that, when wetted, exploded and was projected, burning, from tubes
2.
any of several other inflammable mixtures used in warfare up to the 19th century