What is the meaning of Certain?

Sure in one's mind, positive; absolutely confident in the truth of something.

Not to be doubted or denied; established as a fact.

Sure to happen, inevitable; assured.

Unfailing; infallible.

Fixed; regular; determinate.

Particular and definite, but unspecified or unnamed; used to introduce someone or something without going into further detail.

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.

Named but not previously mentioned.

Used before the name of someone famous that people are expected to know.

Determined; resolved.

Having been determined but not specified.

Unnamed or undescribed members (of).

certain, guaranteed (sure, positive)

certain (specified, particular)

certain (of indefinite, unknown or simply unmentioned identity, quality or quantity)

certain: a determined but unspecified amount of; some

certain; sure

Source: wiktionary.org