If you describe someone as a silent person, you mean that they do not talk to people very much, and sometimes give the impression of being unfriendly.
He was a serious, silent man.
A taciturn person does not say very much and can seem unfriendly.
A taciturn man, he replied to my questions in monosyllables.
Someone who is reticent does not tell people about things.
She is so reticent about her achievements.
Someone who is reserved keeps their feelings hidden.
He was unemotional, quite quiet, and reserved.
If you are secretive, you like to have secrets and to keep your knowledge, feelings, or intentions hidden.
Billionaires are usually fairly secretive about the exact amount that they’re worth.