Definition of "sermonize"
sermonize
verb
third-person singular simple present sermonizes, present participle sermonizing, simple past and past participle sermonized
(intransitive) To speak in the manner of a sermon; to preach; to propagate one's morality or opinions with speech.
Quotations
[…] she would distrust him if she saw him again before he had achieved all his promises; had journeyed clear out to the Mississippi […] and had become fluent in sermonizing in the Dakota language. No, he must see her next in his glory as a practicing missionary.
1949, Sinclair Lewis, chapter 13, in The God-Seeker, New York: Popular Library, page 69
(intransitive) To inculcate rigid rules.
Quotations
If you consider my letters in their true light as conveying to you the advice of a Friend, who sincerely wishes you happiness, and desires to promote your pleasures, you will both read and attend them; but, if you consider them in their opposite, and very false light, as the dictates of a morose and sermonizing Father, I am sure they will be not only unattended to, but unread.
1748, Philip Stanhope, 4th Earl of Chesterfield, Letters to His Son, 6th edition, London: J. Dodsley, published 1775, Volume 1, Letter 106, p. 309