This is the 9166th most frequent Russian word.
серди
"Серди" is the imperative form of the verb "сердить," meaning "make angry" or "provoke anger."
The word 'серди' is used as a part of 'сердитый', meaning 'angry', showing a quality of someone in context.
Серди человека можно увидеть его истинный характер.
In the anger of a person, one can see their true character.
Here, 'серди' is an imperative form of the verb 'сердить', used to command not to make someone angry.
Не серди меня без причины.
Do not anger me without any reason.
'Серди' here is again used in imperative form to instruct someone to incite anger deliberately.