certain

1. (euphemistic, preceded by "a") Used to denote that the speaker is referring to a specific person or thing that they do not want to name directly, implying that the listener should infer the identity of the referent.Examples: "I would have been here on time, but a certain someone lost the car keys!"euphemistic

2. (preceded by "a", of a person) Named but not previously mentioned.Examples: "Looking inside the cover, they learned that the book had once belonged to a certain R. Jones."; "About 140 years ago, for example, a certain Hsü Kuang-ming established an ancestral estate in Wanluan consisting of ten hectares. The trust was specifically set aside to provide for his own worship after death, and access to its profits was to be enjoyed only by his descendants."Synonyms: one

3. (preceded by "a", of a person) Used before the name of someone famous that people are expected to know.Examples: "Since the last British government to make such a proposal was that of a certain Margaret Thatcher, it might not seem unreasonable."Synonyms: one

4. (obsolete) Determined; resolved.Examples: "However I with thee have fixt my Lot, Certain to undergoe like doom[…]"obsolete