Btw hmmm. I did not say plate armor. From myarmoury:
Stiletto (or Stylet)
A short dagger with triangular- or square-sectioned blade that was strong, slender, and sharply pointed. The name seems to stem from the word "stylus," a small pointed instrument used since ancient times for writing and drawing on wax tablets. Because this easily concealed weapon was designed exclusively for delivering thrusts, it was often prohibited in peacetime in towns and cities. Nevertheless, it was a very widespread weapon in the period when mail and leather were used in civil life to protect the body, because it could easily pierce these defenses with a swift stabbing blow.
About the prostitute dagger: They were not just for prostitutes but it seems they were commonly used by them. They are also called lady dagger or garter dagger for that reason.