Random Sequence: asseveration explanation

"She gave Marie a full account of her father's unflattering portrait of Miss Dupont's supposed betrothed; the predictions of ruin in store for him and for her, if she married him, dwelling longest upon the asseveration that he would horsewhip Lorraine if he ever presumed to lift his eyes to one of his daughters."
--"Nobody to Blame" by Marion Harland, in Godey's Lady's Book and Magazine, April 1864

(I found a bound copy of several issues of Godey's in my basement and have been flipping through the dusty pages.)

asseveration (noun) = an earnest, solemn, or emphatic declaration
 
I guess whenever you're talking about "horsewhipping" someone, you're always making an asseveration.