On the Slightest Pretext Meaning?

without any hesitation, delay or preparation ; instantly ; at the slightest signal/urging/pretext/provocation. Note: Probably alludes to the late 19th century common practice of signaling the start of a race or other contest by either dropping a hat or sweeping it in a rapid downward motion.

Is it on the pretext or in the pretext?

pretext for: The conflict was used as a pretext for introducing military rule. on​/​under the pretext of doing something: He visited her on the pretext of borrowing a book.

What dies on the pretext mean?

/ˈpri·tekst/ a pretended reason for doing something that is used to hide the real reason: He called her on the pretext of needing help with his homework.