The most common and most likely answer to this crossword clue is the 5 letter word BARER
I've seen this crossword clue in The Guardian
B
A
R
E
R
More clues leading to the result BARER
Buddy explains!
The straight part
We know that "lesson in two parts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lesson in two parts = barer.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 BARER mean?
BARER adjective- Minimal; that is or are just sufficient.
- Naked, uncovered.
- Having no supplies.
- Having no decoration.
- Having had what usually covers (something) removed.
- (Toronto) A lot or lots of.
- With head uncovered; bareheaded.
- Without anything to cover up or conceal one's thoughts or actions; open to view; exposed.
- Mere; without embellishment.
- Threadbare, very worn.
- Not insured.
- One who bares or exposes something.