A Pillarian slip was a term to describe when an individual inadvertently said something that displayed their inward feelings towards the person or object they were referring to. This was the equivalent to the Human concept of a "Freudian slip", originated by Doctor Sigmund Freud.

In 2152, Doctor Phlox noted that Captain Archer had exhibited two Pillarian slips in the span of thirty seconds, taking it as an indication that Archer was harboring a repressed sexual attraction to Sub-Commander T'Pol. (ENT: "A Night in Sickbay")

This term was named for Executive Producer Michael Piller. [1]; Star Trek Encyclopedia (4th ed., vol. 2, p. 147)