This is a noun: the act of telling someone, in a serious or quite stern way, that they have done something wrong. A parent, a teacher, or a boss might give an admonishment — not a shout, and not a joke, but a clear ‘that was wrong, and you should not do it again.’ It is rather formal and a little old-fashioned. In everyday talk people more often say a telling-off, a warning, or ‘she told him off.’ You will meet admonishment in writing, in news, or when someone wants to sound careful. It sits very close to admonition; many writers prefer admonition. Though actually, speakers mix the two: some feel admonishment names the scolding itself, while admonition can also sound like advice not to do it.