In French une paillasse /pajas/ is a straw mattress, draining board or laboratory bench and un paillasse is a clown. The former is a combination of paille (straw) plus the suffix -asse. Paille comes from the Latin palea, from the Ancient Greek πάλλω (pallo = to shake) because you have to shake the straw to extract the grain. The latter comes from the Italian pagliaccio (clown).
The word paillasse /ˈpalɪas/, meaning a straw mattress, is also used in English and was used in Scots.
Paillasse also appears in des pommes (de terre) paillasses, a potato-based dish which came up in a quiz yesterday.