A spoken lesson or exposition, usually delivered to a group.

“During class today the professor delivered an interesting lecture.”

(by extension) a class that primarily consists of a (weekly or other regularly held) lecture (as in sense 1) [usually at college or university]

“Lecture notes are online.”

A berating or scolding.

“I really don't want you to give me a lecture about my bad eating habits.”

To teach (somebody) by giving a speech on a given topic.

“The professor lectured to two classes this morning.”

To preach, to berate, to scold.

“Emily's father lectured her about the importance of being home before midnight.”