Slip

"Slip" (glisser [vb], glissement [n.])

Lacan uses the verb "slip" -- and its corresponding noun, "slippage" -- to describe the unstable relationship between the signifier and the signified.

Signification - Lacan and Saussure

The term thus emphasizes the different ways in which Saussure and Lacan conceive of signification; for Saussure, signification was a stable bond between signifier and signified, but for Lacan it is an unstable, fluid relationship.