Passalus was one of the Cercopes (with his twin brother Acmon), both being the sons of Oceanus and Theia. His name clearly seems to mean 'peg' or else 'gag' (passalos). We know that Heracles tied both the dwarfish creatures to a pole and carried them off, head down, over his shoulder, and this could be the 'peg' reference, since passalos itself is based on the verb pegnymi meaning 'to fix in', 'to be fixed', 'to be impaled'.

The 'gag' alternative seems harder to justify: Heracles certainly did not succeed in gagging the Cercopes, since even when suspended from his pole they made ribald jokes about his hairy posterior.