In the 1500s, someone who fought bravely, especially against tough opponents, was thought of as being on fire. The flaring of the human spirit that happened when someone acted bravely was compared to tinder bursting into flames. In Scotland, tinder was often a dry, spongy wood that was called ‘spong’ because it looked like a sponge (‘spong,’ the Scottish Gaelic name for a sponge, developed from the Latin word ‘spongia,’ which also meant ‘sponge’). The image of that spongy wood bursting into flames inspired English speakers to turn ‘spong’ into ‘spunk.’