The most common and most likely answer to this crossword clue is the 8 letter word PERORATE
P
E
R
O
R
A
T
E
More clues leading to the result PERORATE
- Waffle about god endlessly, then finish speaking
- Waffle about love endlessly, then finish speaking
- Spout as star losing head, interrupting chatter
- Give a lecture that’s riddle without sounding loud
- Speak at length, offering tattle about the Queen, nothing extra
- Roll or repeat waffle?
- Make a formal speech contributing to camper or a tent
Buddy explains!

The straight part
We know that "Give a lecture" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case give a lecture = perorate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PERORATE mean?
PERORATE verb- To speak or declaim at great length, especially in a pompous or grandiloquent manner; to harangue.
- To make a peroration; to make a formal recapitulation at the end of a speech.