The most common and most likely answer to this crossword clue is the 8 plus 4 letter word DRESSING DOWN
I've seen this crossword clue in The Times
D
R
E
S
S
I
N
G
D
O
W
N
More clues leading to the result DRESSING DOWN
- Drink, getting into gear before lecture?
- Pad, something soft for carpeting
- Vinaigrette to go with miserable rocket
- Covering on the floor is carpeting
- Wearing less than smart apparel invites criticism
- Relish not working – that may bring reprimand
- Mayonnaise gets lower rating
- Rebuking action of person in informal attire
- Thrashing for being less smart?
- Depressed by putting in order for carpeting
Buddy explains!

The straight part
We know that "lecture" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lecture = dressing down.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 DRESSING DOWN mean?
DRESSING DOWN noun- A reprimand or rarely, a thrashing.